
- ,^ 



(lass *?) l!^ ^ Y I 
Book ^76^ f? 



U. S. DEPARTMENT OF AGRICULTURE. 

BUREAU OF ENTOMOLOGY— BULLETIN No. 123. 

L. O. HOWARD. Entomologut and Chief of Bureau. 



A PRELIMINARY REPORT ON THE 
SUGAR-BEET WIREWORM. 



JOHN E. GRAF, 

Entomological Assistant, 
Truck Crop and Stored Product Insect Investigations. 



Issued Fkbuuahy 28, 1914. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1914. 



Monograp/i 



I 



U. S. DEPARTMENT OF AGRICULTURE. 

BUREAU OF ENTOMOLOGY— BULLETIN No. 123 

L. O. HOWARD, Entomologist and Chief of Bureau. 



A PRELIMINARY REPORT ON THE 
SUGAR-BEET WIREWORM. 



JOHN E. GRAF, 

Entomological Assistant, 
Truck Crop and Stored Product Insect Investigations. 



/3 



»~ v) 



/ 



Issued February 28, 1914. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1914. 






BUREA U OF ENTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau. 

C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 

R. S. Cluton, Executive Assistant. 

W. F. Tastet, Chi€f Clerk. 

F. H. Chittenden, in charge of truck crop and stored product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

A. F. Burgess, in charge of gipsy moth and brown-tail moth invcstigatioiis. 

RoLLA P. CuRRiE, in charge of editorial work. 

Mabel Colcord, in charge of library. 

Truck Crop and Stored Product Insect Investigations. 

F. H. Chittenden, in charge. 

C. H. Popenoe, Wm. B. Parker, H. M. Russell, H. O. Marsh, M. M. High, 
Fred A. Johnston, John E. Graf, C. F. Stahl, D. E. Fink, A. B. Duckett, 
F. B. Milliken, entomological assistants. 

I. J. CoNDiT, R. S. Vaile, collaborators in California. 

W. N. Ord, collaborator in Oregon. 

Thomas H. Jones, collaborator in Porto Rico. 

Marion T. Van Horn, Pauline M. Johnson, Anita M. Ballinger, Cecilia Sisco, 
preparators. 



0. OF D. 
MAX 27 ^914 









LETTER OF TRANSMITTAL. 



U. S. Department of Agriculture, 

Bureau of Entomology, 

M'asMngton, D. C, Fehruarij 24, 1913. 

Sm: I have the honor to transmit herewith the manuscript of a 
paper entitled "The Sugar-Beet Wireworm (Limonius californicus 
Mannh.)," by John E. Graf, an entomological assistant of this 
bureau. 

This very active enemy to the sugar beet in the Pacific region has 
been the subject of study in the Bureau of Entomology since 1909. 
The present paper is somewhat preliminary in character, but so many 
facts have been learned that it is believed advisable to submit them 
for publication at the present time. While this wireworm has been 
known in America for many years, no good report of its injuries was 
available until very recently. The paper sets forth the manner of 
injury, the history of the species, the insects associated with it in 
the destruction of the beet roots in different stages of growth, the 
number of its food plants, its life history and habits, suggestions as 
to the methods for its control, and other useful data, and is well 
illustrated. 

I recommend the publication of this manuscript as Bulletin No. 
123 of this bureau and would urge that it be issued at an early date, 
as there is great demand for information on the part of the sugar- 
beet growers of the country, all of whom are more or less troubled 
by the ravages of wire worms. 

Respectfully, :,- . C. L. Marlatt, 

Entqmdlqgisf and Acting Chief of Bureau. 

Hon. James Wilson, '*" " ''"' 

Secretary of Agriculture. 

3 



PREFACE. 



The present bulletin is intended as a preliminary report of the 
investigations which have been carried on with the sugar-beet wire- 
worm (Limonius califomicus Mannh.) since 1909. The life-history 
work has not been completed; in fact it was not until the spring of 
1912 that it could be started on a scale which gave any promise of 
ultimate success. As tests of many of the control measures were 
finished during the latter part of 1912, and as it will be several years 
before a complete study can be finished, it has been decided to 
publish a report at this time givmg all the observations and experi- 
ments which have been carried on thus far. 

During the coming years, in addition to the completion of the 
life-history studies, work will be carried on with other control 
measures. The relation of the birds of the sugar-beet fields to the 
wireworms will also be investigated, as will the bacterial and fungous 
diseases which have been observed to affect this species. 

The author wishes to acknowledge his indebtedness to Dr. F. H. 
Chittenden and Mr. H. M. Russell for assistance and suggestions 
throughout the work. Mr. Russell began the study of Limonius 
califomicus in 1909. The cooperative work of Mr. R. S. Vaile, of 
the Ventura County horticultural commission, and Prof. H. S. 
Fawcett, of the University of California, is also deserving of grateful 
acknowledgment. 

J. E. G. 
5 



CONTENTS. 



Page. 

Historical il 

Losses due to the sugar-beet wireworm 11 

Insects found with the sugar-beet wireworm 12 

Classification, synonymy, and common names 13 

Descriptions 14 

The adult 14 

The egg , 14 

The larva 14 

The pupa 15 

Distribution K) 

Food plants 10 

Life history and habits 18 

The egg 18 

Time and place of deposition 18 

Number and hatching of eggs 19 

Length of egg stage 20 

The larva. 20 

Emergence from the egg 20 

The newly hatched larva 20 

Rearing cages used 21 

Habits of the young wireworms 22 

Approximate length of larval stage 24 

Habits of the older wireworms 25 

Location of food by the wireworms 25 

Activity of the wireworms 26 

Wireworm injury to beets 26 

Time the wireworms can live without food 27 

Relation laetween injury in the beet fields and the size and abundance 

of wireworms 29 

Molting of the wireworms 29 

The pupa 30 

Pupation 30 

The pupal cell 30 

Soil conditions affecting pupation 30 

Vitality of the pupa 31 

Changes in color of the pupa 31 

Length of the pupal stage 31 

The adult 32 

Emergence of the adult 32 

Period of emergence 32 

Actions directly after emergence 32 

App'earance of beetles in the spring 33 

Beginning of the period of activity 33 

Variation in the size of beetles 34 

7 



8 THE SUGAE-BEET WIREWORM. 

Life history and habits — Continued. 

The adult — Continued. Page. 

Variation in the color of l^eetles 34 

Feeding of the adults, and food plants 35 

Styles of rearing cages used 36 

Duration of life under varying conditions 37 

Length of time adults can be submerged 38 

Effect of temperature on the adults 39 

Ability of the adults to withstand unfavorable conditions 40 

Method and time of mating 40 

Actions of the adults after mating 41 

viposition 42 

Approximate length of the life cycle 42 

Seasonal historj-' 42 

Beetles from emergence to hibernation 42 

Hibernation 43 

Mortality during hibernation 43 

Gradual emergence from hibernation 43 

Secondary hibernation 44 

Occurrence of beetles in the field 45 

Effect of food in the field on dissemination 45 

Other factors governing dissemination 46 

Natural control 46 

Enemies and checks to the beetles 46 

Enemies and checks to the larvae 48 

Fungi affecting the pupse and eggs 49 

Remedial measures 50 

Historical 50 

Tests of suggested remedies against the sugar-beet wireworm 50 

Attempts to destroy the adults with poisoned baits 50 

Fall plowing for destruction of the pupae 51 

Experiments with deterrents against the wireworms 52 

The use of potassium cyanid against the wireworms 59 

Experiments with poisoned bait against the wireworms 60 

Experiments with guano fertilizer 61 

Protection of beets by early planting 61 

Clean culture against the adults 61 

Summar}^ 64 

Bibliography 64 

Index 65 



ILLUSTRATIONS. 



PLATES. 

Page. 
Plate I. Adults of the sugar-beet Mnreworm (Limonius calif omicus) , showing 

variation in size 12 

II. Stagesof the sugar-beet wireworm. Fig. a. — Adult. Fig.b. — Newly 

hatched larvae. Fig. c. — Eggs 12 

III. A sugar-beet wireworm in process of molting. 12 

IV. Wireworms and wireworm-like larvae 12 

V. Pupa of the sugar-beet wireworm 16 

VI. Injury by the sugar-beet wireworm to germinating beans 16 

VII. Injury by the sugar-beet wireworm to germinating bean, enlarged. . 16 
VIII. Fig. 1. — Sugar-beet wireworms in petri dish, killed by bacteria in 
cultures of agar. Fig. 2. — Root cage used in rearing young wire- 
worms * 20 

IX. Work of the sugar-beet wireworm. Young sugar-beets, showing 
injury by wireworms to taproots; blackened feeding marks visible 

on end of roots 24 

X. Work of the sugar-beet wireworm. Nearly mature beets killed by 

wireworms; blackened feeding marks noticeable on taproots 24 

XI. Work of the sugar-beet wireworm. Mature beets, showing old scars 

resulting from wireworm injury 24 

XII. Ravages of the sugar-beet wireworm. Beet field, showing small 

cleared space resulting from the work of wireworms 24 

XIII. Ravages of the sugar-beet wireworm. Beet field, showing cleared 

spaces resulting from the work of wireworms 24 

XIV. Ravages of the sugar-beet wireworm. Beet field, showing cleared 

spaces, more extensive than in Plate XIII, resulting from the work 

of wireworms 24 

XV. Ravages of the sugar-beet wireworm. Beet field, showing very large 

cleared space resulting from the work of wireworms 24 

XVI. Adult of the sugar-beet wireworm issuing from pupal skin 32 

XVII. Habits of beetles of the sugar-beet wireworm. Fig. 1. — Beetles of 
the sugar-beet wireworm in secondary hibernation under slice of 
sugar beet. Fig. 2. — Beetles of the. sugar-beet wireworm photo- 
graphed while feeding on slices of sugar beet 32 

XVIII. Secondary hibernation of the sugar-beet wireworm. Beet tops used 

by beetles as quarters for secondary hibernation 36 

XIX. Fig. 1. — Field of yoiuig beets at age when they begin to be partially 
safe from severest injury by the sugar-beet wireworm. Fig. 2. — 
Beet field showing conditions favorable for increase of wireworms. 

Weed hedges which shelter adults in secondary hibernation 60 

XX. Conditions favoring the sugar-beet wireworm. Beet field imme- 
diately after harvest, showing beet tops carelessly scattered over 

ground 60 

9 



10 THE SUGAR-BEET WIEEWOEM. 

Page. 
Plate XXI. Clean culture against the sugar-beet wire worm. Natural method 
of clearing off beet tops, by pasturing cattle in the field, 

which has been inclosed by a temporary fence 60 

XXII. Clean culture against the sugar-beet wireworm. Collecting the 
beet tops in piles and hauling them from the field as food for 

stock 60 

XXIII. Conditions favoring the sugar-beet wireworm. Fig. 1. — Beet 
fields separated by a strip of alfalfa. Fig. 2. — Field of alfalfa 
adjoining field of sugar beets 60 

TEXT TIGURES. 

Fig. 1. The sugar-beet wireworm (Limonius californicus). Details of larva. 15 

2. Map of California showing counties from which the sugar-beet wire- 

worm has been reported 17 

3. Injiu-y by sugar-beet wireworm to field of sweet corn, Dominguez, Cal. 18 

4. Diagram showing the period eggs of the sugar-beet wireworm were in 

the soil, with temperature; season of 1912, Compton, Cal 19 

5. Janet ants'-nest plaster-of-Paris cage, used in rearing sugar-beet 

wireworms 22 

6. A sugar-beet wireworm devouring one of its own kind; to illustrate 

cannibalistic habit ". 25 

7. Diagram showing length of life of sugar-beet wireworm without food . . 28 

8. Screen cage used in observing oviposition of adults of the sugar-beet 

wireworm under field conditions 36 

9. Diagram of beet fields, to illustrate the effect of clean culture in 

reducing injury by the sugar-beet wireworm 63 



THE SUGAR-BEET WIRE WORM. 

(Limonius californicus Mannh.) 



HISTORICAL. 



The sugar-beet wireworm (Limonius californicus Mannh.) has been 
known in the coast lowlands of southern California for many years, 
having been more or less destructive to sugar beets during the time 
they have been grown here, and prior to that time was known as an 
alfalfa and corn pest. In many locaUties the alfalfa had to be 
plowed up and replanted every few years, as the ravages of this larva 
so tliinned it out that only a partial crop could be harvested unless 
replanting was resorted to at intervals. Owing to the fact that the 
ground in the alfalfa fields is nearly always damp to the surface, the 
wire worms seldom worked deep, and wliile they tunnelled through 
the crown of the plant, it was only a chance injury or a heavy infesta- 
tion that could make itself felt, so that its destructive powers in the 
alfalfa fields is proof enough of its abundance. 

The wireworm has also been noted as a corn pest for years, many 
growers reporting that on occasions it has been impossible to secure 
an average crop even with several plantings. Mr. Nelson Ward, of 
Compton, reports that on pulling up cornstalks he has discovered 
from 17 to 30 wireworms burrowing through the roots and into the 
crown of a single plant. 

LOSSES DUE TO THE STTGAR-BEET WIREWORM. 

There is great variation in the estimates of losses ascribed to this 
insect, and very probably the correct estimate would run far above 
the others. The reason for tliis is that unless the injury is excep- 
tional it is hkely to go entirely unnoticed. When the wireworms 
work scatteringly, their injury is apparent only to the observer who 
is looking especially for it, and at the right time. The wi'iter bases 
this assertion on observations made during the early spring of 1912. 
At this time the adults were being collected, and as several hundred 
acres of beet fields were carefully gone over several times, it was 
possible, by close observation, to get a good estimate of the progress 
of the injury and the total damage done. 

The sugar beets were quite small, having just been tliinned, and 
were consequently at just the right age to receive the greatest injury. 
The roots were simple, not having swelled, and wherever a beet plant 
was attacked it was generally killed, as the roots were almost invari- 
ably severed by the feeding of the wireworms. All the plants which 
were noted wilting down were examined, and always with the same 

11 



12 THE SUGAR-BEET WIREWORM. 

result, viz, the tender taproot was cut and blackened and a searcli 
generally revealed the offender, a wireworm, in the soil near by. A 
great amount of just such work was noted, but it differed from that 
of 1911 in that it was more scattered. 

In 1911 the wireworms seemed to be working in groups, and many 
spots of var^^ng size were completely cleared of beets. In 1912, 
however, the fields were almost entirely free from tliis type of work. 
Places were observed where from three to six beet plants had been 
killed in one group, but by the time the beets are mature their foliage 
so covers the ground that all trace of the injury is lost to the casual 
observer. One incident will illustrate this point. A small beet field 
of 10 acres located near the laboratory was carefully watched that 
some idea might be gained of the progress and time of injury. Every 
day many of the plants were found dead, but seldom were more than 
three or four plants killed in a place. While this injrry was con- 
siderable it was kept well scattered. At the time of the last examina- 
tion the beets, then nearly ripe, so covered the ground with their 
fohage that even where several adjoining plants had been killed it 
was difficult to find any signs of the injury. This shows that it is 
an easy matter to overlook the destructive power of this wireworm. 

The sugar-beet wireworm may be considered the worst insect 
enemy of the sugar beet in southern California at the present time. 
It has this distinction for two reasons: First, it is constant, appearing 
every year to a greater or less extent; and, second, its injury occurs 
in such a manner that replanting is generally impracticable, or at 
least of little value. While beets and alfalfa appear to be the favorite 
food plants, the sugar-beet wireworm is also very injurious to corn 
(fig. 3, p. 18) and beans (Pis. VI, VII). 

It would be a difficult matter to figure the loss due to the wire- 
worm, either in percentage of the crop, tons, or dollars, but an 
approximation will show its importance economically. Mr. R. S. 
Vaile, horticultural commissioner of Ventura County, in his annual 
report for 1912, places the loss to lima beans alone in his county at 
$10,000. For 1913 he estimates the loss at $25,000 or more. If 
the other counties where this wireworm is destructive are taken 
into consideration it will be seen that probably the hma-bean growers 
alone lose at least $50,000 a year by this insect. Add to this the loss 
to sugar beets, which is probably even greater, and it is readily seen 
that tliis wireworm presents no small problem in southern California. 

INSECTS FOUND WITH THE SUGAR-BEET WIREWORM. 

Collections of wireworms in the beet fields of southern California 
show at a glance that they are made up of several species. These 
differ widely in appearance, hence there is little chance of their being 
mistaken for one another. Two of them, Limonius californicus Mannh. 
and Drasterius livens Lee, are of the waxy color usually found in 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate I. 





Adults of the Suqar-Beet Wireworm (Limonius californicusi, Showing Varia- 
tion IN Size. (Original.) 



Il 



Bill. 123, Bureau of Entomology, U. S. Dept of Agriculture. 



Plate II. 




« 



Stages of the Sugar-Beet Wireworm. Fig. a— Adult. Fig. ft.— Newly Hatched 
Larv/e. Fig. c— Eggs. (Original.) 



Bui. 123, Bureau of Entomology. U. S. Dept of Agriculture. 



Plate III. 




A SUGAR-BEET WIREWORM (LIMONIUS CALIFORNICUS) MOLTING; THE CaST-OFF 

Skin Showing near the Anal Plate. iOriginal.) 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate IV. 




WIREWORMS AND WiREWORM-LiKE LaRV/£; THE SUGAR-BEET WiREWORM (LIMONIUS 

Californicus) being the Third Larva from the Left, and the Large One at 
THE Right being a False Wireworm. Above is a Dipterous Parasite. 
Magnified. (Original.) 



CLASSIFICATION, SYNONYMY, AND COMMON NAMES. 13 

wireworms. The latter is considerably the smaller of the two, and 
only an occasional individual has come under observation. The 
other wireworms are white, with a slight yellow tinge. Two of them 
belong to the genus Cardiophorus, one having been identified by Mr. 
E. A. Schwarz, of this bureau, as Cardiophorus xneus Horn. The 
other has not yet been reared, but as several adult specimens of 
C. crinitus Blanch, have been taken in the fields, it is probable that 
it belongs to this species. The other wireworm found in the fields 
is a large, robust, wliitish one, considerably larger than Limonius 
californicus. This has not been reared and remains undetermined. 

In the spring, when the adults are found in the beet fields, four 
other elaterids are found with them, though in lesser numbers. The 
most common one resembles in general characteristics Limonius 
californicus. It is of about the same size and outline, but differs 
from L. californicus in the color of its elytra, which are a decided buff 
instead of a deep brown. Dr. Chittenden has stated that this may 
prove to be a new variety of californicus, since, while it resembles that 
species quite closely, it seems to disagree in several small particulars. 
From the numbers of these which were found with L. californicus it 
is possible that they may be of economic importance. This species 
may be called the lesser sugar-beet wireworm to distinguish it from 
L. californicus. 

The other elaterids which were found occurred in very small num- 
bers, so that they may be disregarded from an economic standpoint. 
These have been determined as Drasterius livens, Cardiophorus seneus, 
and C. crinitusi ?). These three are considerably smaller than X. cali- 
fornicus and there is therefore little chance of their being mistaken 
for the latter. 

Another beetle commonly noted in the fields is a carabid, Platynus 
sp., sUghtly larger than L. californicus, robust, black in color, with a 
slight metallic tinge. 

Two species of tenebrionids are also commonly found with Limorb- 
ius californicus. Both are short, very robust, and dull black in color. 
One is Blapstinus sp., the other a species of Coniontis. 

CLASSIFICATION, SYNONYMY, AND COMMON NAMES. 

Limonius californicus (PL I; PI. 11, fg. a) belongs to the common 
genus Limonius of the family Elaterid^e. It further belongs to the 
tribe Elaterini and group Athoi. 

It was described from America in 1843 by Mannerheim as Cardio- 
phorus californicus and has since been referred to the genus Limonius. 
Cardiophorus californicus is its only known synonym. 

The larvae of this entire family of insects are commonly known as 
wireworms. The adults, due to their habit of throwing themselves 
into the air when placed on their backs, have received the names 
"skipjacks," "cUck-beetles/' ''spring-beetles," and "blacksmiths." 



14 THE SUGAR-BEET WIREWOEM. 

DESCRIPTIONS. 

The Adult, 

Following is the original description by Mannerheim ^ in Latin, 
followed by a translation into English. 

136. Cardiophorus californiais: elongatus niger, punctatissimus, tenue pubescens, 
thorace convexo, subqiiadrato, elytris dorso depressis, le\'iter punctato-striatis, 
sterno profunde punctate, convexo, tarsis articulis omnibus et unguiculis simplicibus. 

Longit. 5J, 4J lin. latit. If, If lin. 

Habitat in California, D. D. Blaschke et Tscliernikh. 

[Translation.] 

Cardiophorus californicus: Elongate black, closely punctate, finely 
pubescent; thorax convex, subquadrate; dorsal surface of elytra de- 
pressed, feebly striate-punctate ; thorax beneath deeply punctate, 
convex; all joints of the tarsi and claws simple. 

Length lOf-9^ mm., width 3j-3^ mm. 

Habitat, Cahfornia (Blaschke and Tschernikh). 

The Egg. 

The egg of Limonius californicus (PL 11, fg. c) is for the most part 
opaque white, though it shows small, irregular, semihyaline areas 
when placed on a white surface in dim Ught. The surface appears 
smooth under the low power of the microscope, but under the liigh 
power it appears to be sHghtly scaly. It reflects Ught weakly from 
the lighted side. That the shell is quite tough is proven by the fact 
that even when the eggs are rolled about in the soil they are seldom 
distorted. 

The egg is ellip to-cylindrical in shape. Both ends are broadly 
rounded and resemble each other. Measurements of 30 eggs gave 
an average length of 0.69 mm. and an average width of 0.5 mm. 
The length varied between 0.63 and 0.735 mm. and the width be- 
tween 0.473 and 0.53 mm. 

The Larva. 

The nearly mature larva of Limonius californicus (fig. 1; PI. II, 
Jig. h; Pis. Ill, IV) is subcyhndrical in shape and shiny, waxy yeUow- 
ish-brown in color. The segments are very minutely and sparsely 
punctate. The head and venter are flattened dorsally and darker in 
color. There is a light dorsal stripe on the posterior end of each seg- 
ment with the exception of the venter. 

The head is depressed and considerably narrower in front. The 
mandibles are strong, notched, deep brown in color, changing to 
black at the tip. 

» Bui. Soc. Imp. Nat. Moscou, vol. 16, p. 238, 1843. 



DESCRIPTIONS. 



15 




The first thoracic segment is broad and long, being about equal 
in length to the venter. The other thoracic segments are short, 
being about equal in length to the first two abdominal segments. The 
remaining abdominal segments are a little longer and quite similar. 
The legs are short and armed with heavy, short brown spines. 

The abdominal segments are slightly constricted where they join 
one another. There are from two to four hairs on the lateral side of 
each segment. The spiracles are brown, conspicuous, and are 
situated in a poorly defined, light lateral stripe. They are shghtly 
nearer the anterior end of the segment. 

The venter is depressed dorsally, with raised edges. It is sparsely 
hairy around the edge. The caudal notch has a small tooth on each 
side pointing shghtly 
upward and backward. 
The margin of the 
notch varies from deep 
brown to black. 

The average length of 
the mature larva is from 
18 to 21 mm., and the 
width is from 2.5 to 
3 mm. 

The Pupa. 

When first formed the 
pupa is opaque white, 
but after a time the 
eyes show through as 
pale, dusky, blue spots. 
About this time the tho- 
racic segments become 
a pale waxy yellow, but 
no other changes take 
place until shortly be- 
fore emergence. 

The pupa (PI. \.) very much resembles the adult beetle in shape, 
except that the abdomen is slightly longer in the pupal stage. The 
head is bent forward slightly, and each anterior angle is armed with 
a long, heavy spine, which tapers regularly to a point. The mouth 
parts are conspicuous. The antennse are laid along the margin of 
the head on the ventral side, and their tips are behind the tibiae of 
the second pair of legs. On the underside of the head and near the 
prothorax are two short, heavy spmes. There are also two short, 
stout spines on the dorsal side of the head near the posterior angles. 

The case covering the springing apparatus is plainly visible 
between the anterior coxae. The leg cases are folded similarly to 





Fig. 1.— The sugar-beet \vireworm(Z,zmon;M.9ca/!/oraJCMs): a, Head; 
6, anal segment from above; c, same, lateral view. Highly mag- 
nified. (Original.) 



16 THE SUGAR-BEET WIKEWOKM. 

those of other Elaterida\ All of the posterior pair, excepting the 
tarsi, are covered by the wing cases, which are curved around and 
almost meet on the ventral side, at the distal end of the third abdomi- 
nal segment . 

The abdomen is contracted sharply at the seventh segment, so 
that the eighth segment is only a little more than haK as wide as 
the anterior end of the seventh. 

The anal segment bears two long, heavy spines on its posterior 
angles. These spines are shghtly divergent, are pitted, and the 
distal half of each is brown, changing to black at the tip. 

The pupaB vary greatly in size. Measurements taken from sev- 
eral individuals give an average length of 11.5 mm. and a width of 

3.6 mm. 

DISTRIBUTION. 

This wireworm is found quite generally throughout the western 
haK of California. It is abundant in the lower sugar-beet lands of 
southern Cahfornia. The main districts affected by it are those of 
Ventura, Orange, and Los Angeles Counties. These three districts 
comprise probably the choicest sugar-beet land in southern Cali- 
fornia. The station for the study of this insect was located in 
Compton, in Los Angeles County, about 10 miles from the coast, 
and surrounded by about 12,000 acres of sugar beets. 

Limonius californicus has been reported from the following 
places, all in California: Riverside, San Bernardino, Los Angeles, 
Lake, Monterey, and El Dorado Counties, by Prof. H. C. FaU; near 
Owens Lake, collected by Dr. A. Fenyes; Marin County, specimens 
in the collection of the University of California; Orange, Ventura, and 
San Diego Counties. (See fig. 2.) 

Prof. A. L. Melander, entomologist of the Washington Agricultural 
Experiment Station, Pullman, Wash., reports that in the collection 
there they have a single specimen which was collected in eastern 
Washington. 

It is thus seen that this species is fairly well scattered along the 
western half of California. It is probably not of economic impor- 
tance outside this State. 

FOOD PLANTS. 

The larvae of Limonius californicus have been noted to feed on 
the following plants: 



Sugar beet. 

Wild beet {Beta sp.). 

Potato {Solamnn tuberosum). 

Lima bean (all varieties). 

Com (all varieties). 

Johnson grass {Sorcjhiiin halepense). 

Dock {RiDiifx hymenosrpalus). 



Alfalfa ( Medicago spp.). 

Pigweed (Amaranthus retrofiexus) . 

Chrysanthemum . 

Nettle (reported by H. M. Russell). 

Wild aster (reported by H. M. Russell). 

Mustard {Biasska niger). 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate V. 




Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate VI. 




123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate VII. 





mmt^ 


4'^3c 


» 


s \ 



-ir-v- 



!«•«;•; 



FOOD PLANTS. 



17 



It is difficult to note a preference of this wireworm for any par- 
ticular food plant, as sugar beets, lima beans (Pis. VI, VII), corn 
(fig. 3), potatoes, and aKalfa aU seem to be favored. After these 




Fig. 2. — Map of California showing counties from which the sugar-beet wireworm has been reported. 

(Original.) 

ill order come Johnson grass and wild beets. The remaining food 
])lants seem to be taken more from necessity than choice, and it is 
only occasionally that larv« are discovered feeding on them. :, 

6140°— Bull. 123—14 2 



18 THE SUGAR-BEET WIREWORM. 

LIFE HISTORY AND HABITS. 

The Egg. 
time and place of deposition. 

The eggs (PI. II, jig. c) arc all deposited during the spring and in 
the greatest numbers about th(^ middle or latter part of April. (See 
diagram, fig. 4.) During the latter ])art of March immature eggs 
to the number of from 25 to 40 could be dissected from the swollen 
abdomens of the females. 

On A])ril 9 the first eggs W(u-e laid. These were placed in the 
loose damp soil of the rearing cages, about 1^ inches below the 




Fig. 3. — Injury by sugar-beet wirewomi {Limonius califnrnk.us) to field of sweet corn, Dominguez, Cal. 

(Original.) 

surface. It seems that it is intended that the eggs shall always be 
placed singly, as out of about 8,000 eggs taken from the soil only a 
very few cases were noticed where several eggs were together. Never 
were more than three eggs in a grou]i, and these were not held together 
in any way. 

Food plants seem to have no effect on the place of deposition, as 
there were always as many eggs found at the edges of the cage as 
there were surrounding the young beet plant at the center. At first 
this was supposed to be due to the fact that the tender root hairs 
are scattered rather generally through the soil, but later tests seemed 
to indicate that the place of deposition is affected more by the con- 



LIFE HISTORY AND HABITS. 



19 



ditioii of the soil, a loose damp soil being selected by the adults in 
preference to other kmds. 

Nearly all the eggs were placed in the first inch and a half of damp 
soO, and the greater part of these about 1 inch below the line of 
dampness. 

A small mite, which has been identified by Mr. Nathan Banks as 
(Gam^sus) Parasitus coleoptratorum'L. (?), was commonly noted in the 
soil Avith the eggs but was never seen destroying them. 

NUMBER AND HATCHING OF EGGS. 

Complete records for the eggs could not b(; obtained, so the num- 
ber of eggs laid by a female of this species is still a (juestion. One 
female which had been isolated after fertilization laid 71 eggs before 
death, and 11 were added by dissection, bringmg the total to 82 
eggs. Another female gave a total of 63 eggs by oviposition and dis- 
section. Two others gave 61 and 52 eggs. Twenty-five dissections 
gave the number of eggs as between 28 and 40, or an average of about 



Afy^y 




Fig. 4. — Diagram showing the period eggs of the sugar-beet wireworm were in the soil, with temperature: 
season of 1912, Compton, Cal. (Original.) 

34 eggs })er individual. It is (piite probable that 100 eggs or even 
more may be deposited by a smgle female. 

Practically all the eggs hatch. In the laboratory over .94 per 
cent of 5,000 eggs hatched successfully, even after they had been 
handled and kept under artificial conditions. Those which did not 
hatch were for the most part either allowed to dry out or were killed 
by a fungus. Elimmating two cages — the one which dried out and 
the one in which the fungus appeared — it would be safe to say that 
over 98 per cent of about 4,200 eggs which were kept under labora- 
tory conditions hatched safely. 

There is an optimum zone, in so far as the degree of dampness is 
concerned, for the hatchmg of the eggs. Some eggs kept in a drv 
vial indoors, where it was not too warm, failed entirely to hatch and 
after a time shriveled up. On the other hand, the eggs which were 
kept too damp were subject to a fungous attack. Water itself 



20 THE SUGAE-BEET WIKEWORM. 

seems to have little effect on the hatching of the eggs, as some which 
were kept partially submerged part of the time hatched in good 
shape. 

As hatching time approached, large, UTegular, hyaline areas ap- 
peared in the eggs in various places. At first nothing could be seen 
of the embryo, but about a week before hatching its outlines could 
be made out with difficulty. The embryo became little plainer, 
even at the time of hatching. 

LENGTH OF EGG STAGE. 

The length of the egg stage varied under laboratory conditions 
from 23 to 33 days, most of the eggs hatching in from 27 to 30 days, 
so that the length of the egg stage may be roughly considered as a 
month. It seems probable that the period might be shortened mate- 
rially under favorable conditions, out of doors, and eggs laid in the 
warm damp soil might possibly hatch in from 15 to 25 days. 

The Larva. 

emergence from the egg. 

The larvae (PI. II, fg. h) emerge from the eggs by eating a small 
hole in the shell and crawling out. In all the cases noted the hole 
was very little larger than the body of the wireworm, so that it is a 
matter of a few moments for the young wu-eworm to leave the shell 
entirely. In the case of several which were timed, between two and 
seven minutes elapsed from the appearance of their heads through 
the shell until they were entirely free. During the earlier j)art of the 
hatchmg season no eggshells could be found, and it was thought 
probable that the larva on emerging used the shell for food. Such 
did not prove to be the case, however, as later, when more eggs were 
hatchmg, it was observed that the larva on hatching leaves the old 
shell almost at once. In a few cases the larvae crawled around the 
shells for a short time but did not attempt to eat them and always 
left them intact. Where the eggs are hatching hi the soil, the young 
larva remains for a short time in the cavity occupied by the egg. 
That the eggshells are quite tough was proven by the fact that 
the empty shells were able to retain theh shape for some time. 

THE NEWLY HATCHED LARVA. 

When first hatched the larva (PL II, Jig. h) is semiopaque white. 
The extreme tips of the mandibles are the only parts which show 
any color, and these are light yellow. The general proportions of 
the newly hatched larva are very much like those of the older ones. 
They vary little in size. Then average length is 2 mm. and the 
width is 0.27 mm. 



Bui. 123, Bureau of Entomology, U, S. Dept. of Agriculture. 



Plate VIII. 




Fig. 1 .— Sugar-Beet Wireworms in Petri Dish, Killed by Bacteria in 
Cultures of Agar. (Original.) 





















- - 



















Fig. 2.— a Root Cage Used in Rearing Young Wireworms. (Original.) 



LIFE HISTORY AND HABITS. 21 

When these larvae are exposed to a moderately subdued light they 
color quite rapidly and become noticeably yellow all ovor their 
bodies in a day's time. Wlien the newly hatched larvae are kept in 
darkness they color more slowly, and two or three days elapse before 
their bodies become yellowish. Their skui is quite tender, but in 
spite of this they can survive rather rough handling. 

REARING CAGES USED. 

Several styles of cages were used in an endeavor to find one in 
which the wireworms could be successfully reared and at the same 
time watched. Only three types gave any promise of success, and 
these will be reviewed briefly. 

The first type used was simply a petri dish with damp filter paper 
in it. Several sheets of filter paper were used so that when the 
larvae crawled between the sheets it was almost the same as if they 
were in damp soil. Slices of beets were placed in the cage and 
renewed daily. These were of use not only as food for the wireworms, 
but they also assisted in keeping the atmosphere of the dish damp 
and cool. These dishes were then kept in insect boxes to insure per- 
fect darkness and to assist in keeping the temperature even. This 
style of rearing cage was very successful for the first two weeks, and 
much was expected of it, but from that time on one bad point after 
another presented itself, and within a month the cage was given up 
as impractical. The two worst points in connection with this cage 
are that the amount of moisture can not be regulated and, secondly, 
that there is no drainage and the cage tends to foul easily. The 
cages were cleaned every day and fresh filter paper added, but in 
spite of all these precautions a red bacterium (PL VIII, fig. 1) made 
its appearance in several of the cages at about the same time, and as 
there seemed to be no way to check it this style of cage was given up. 

Another rearing cage (fig. 5) which was used was made of plaster 
of Paris, and was patterned after the Janet ants' nest, except that it 
was more simple. It is a plaster-of-Paris block with two depressions 
in it. Water is kept in one and the wu*eworms m the other. The 
water readily soaks through the block, and if the dish is covered 
with a tight-fitting piece of glass the depression containmg the wu-e- 
worms is kept damp and cool. The cage is further improved by 
painting the glass plate black to exclude light. Dr. Chittenden sug- 
gested a coating of paraffin for the outside of the dish to cut down 
the excessive evaporation. This scheme worked well where only 
part of the dish was coated. Whenever the entire outside of the cage 
was coated, however, the drainage was cut off, the cage became foul, 
and the wireworms died. The great advantage of this cage, as 
pointed out by Messrs. Knab and Dimmock, is that it can be sterilized 
simply by heating. Most of the first trials of this cage were failures, 



22 



THE SUGAR-BEET WIREWORM. 



but it soon giwc promise of being a simple and safe receptacle in 
which to rear wireworms. 

^ The other style of cage was the common root cage (PL VIII, fig. 2), 
so often used for the study of underground insects. The cages used 
in these expeiyments had the glass walls very close together (one- 
eighth to one-fourth inch) so that there would not be much soil in 
which the larvae could hide. The root cages were not so successful 
as it was hoped they would be, for the larvae were usually able to 

conceal themselves and 
it seemed almost im- 
possible to wet the 
cages properly. Used 
in conjunction with the 
other cages, however, 
they gave fair success. 
The majority of the 
young wireworms were 
kept in large flower- 
pots, so that in case of 
accidents to the rearing 
cages not all the larvjc 
would be lost. These 
pots had an added ad- 
vantage in that they provided soil conditions quite similar to those 
out of doors. The flowerpots were emptied and examined from time 
to time so that the larva^ coidd be watched. 




Fig. 5. — Janet ants'-nest plaster-of-P<iri>> cage, used in rearin); 
sugar-beet wireworms. A, compartment for larvse; B, com- 
partment for water. (Original.) 



HABITS OF THE YOUNG WIREWORMS. 

The young wireworms are quite active, moving over smooth sur- 
faces or burying themselves in the loose soil with ease. Some placed 
in a root cage buried themselves almost at once, but were tempora- 
rily checked by a layer of compact earth about an inch below the 
surface. On the followmg day several had entered the compact 
layer and the next day one was noted at a depth of 4 mches. 

A\Tien very young they are unable to survive in dry earth even for 
a relatively short time. Some which were placed in a petri disli 
with dry soil were dead at the end of five hours, a few dying after the 
first hour and a half. 

These larvae shun the light and when exposed to it hide under any 
object which they can find. When placed in the petri-dish cages 
they soon crawl between the layers of filter paper at the bottom. 
Experiments were made to test their ability to locate food, by placing 
a slice of sugar beet in the cages and noting the time it took them to 
collect under it. The beet shce was not larger than a dollar and was 



LIFE HISTORY AND HABITS. 23 

placed in the center of a large petri dish. Within 10 minutes all the 
wireworms were under it. This experiment was repeated by using a 
piece of damp cardboard the size of the beet slice and again timing 
the wireworms. In this test all the larvae finally gathered under the 
cardboard to escape the light, but a longer time was required before 
this took place. These tests were repeated several times as checks 
and always gave the same results, so it is evident that the larvae are 
able, to a small extent, to locate food. 

The larvae begin feedmg noticeably, though lightly, very soon 
after hatching. A fresh sUce of sugar beet was placed m the cage 
every day, and when each slice was removed the minute black feedmg 
marks could be noticed. The depressions made by the feedmg could 
be made out only with a hand lens, but the black stain, so character- 
istic of wireworm injury, had spread out and was quite conspicuous. 

The wireworms grow quite rapidly during the first two or three 
weeks, and it might be added that this is the only time in then- long 
larval life when then- growth is apparent. They approxhnately 
double in size in this time and then remain about the same size until 
they molt. At the time of their first molt they take a sudden jump 
in size and froiii. this time on their growth is very slow. 

An attempt was made to trace the molts with these wu-eworms, 
but unfortunately it had to be abandoned. The death rate in the 
exposed cages was so high that it soon became apparent that none 
could be brought entu'ely through in this manner. Added to the 
difficult}" was the fact that smce theu" time of moltmg was so irregular 
only a few could be kept in a single cage. After about a thousand 
larvae had died m these cages it was concluded that it was impossible 
to carry the observations to completion with the forms of rearing 
apparatus at hand. The cast skins of the larvae could not be found, 
owmg to their small size and transparency, and the only molts that 
could be traced were in the case of certain larv» wlfich increased in 
size quite noticeably overnight. The increase in the width of the 
head was found to be the best test. 

From time to tune the soil in the flowerpots containing the bulk of 
the wireworms was carefully examined to see whether anything could 
be learned concerning the feeding habits of the larvae under natural 
conditions. In every case the larvte were found scattered rather 
generally through the soil, and as many of them were found around 
the edges of the pot as directly around the beet root. Since the root 
hairs were scattered pretty generall}" through the soil it seemed prob- 
able that the lai'vae fed on them. This was further indicated by the 
fact that no feeding marks could be found on the main beet root. 
At any rate it is safe to say that, from the standpoint of injury due 
to their feeding, the wireworms during the first year of their larval 
life may be disregarded. Larvae were generally found from 1 to 3 



24 THE SUGAR-BEET WIREWOEM. 

inches below the surface, but as the soil in the rearing cages was 
kept damp to the surface they would evidently be found deeper under 
field conditions. 

Examination from time to time during the summer revealed no 
startling changes. Growth was very slow, but the wireworms bo- 
came more active, and their skins a deeper yellow and noticeably 
harder. 

APPROXIMATE LENGTH OF LARVAL STAGE. 

As the first larvaB of this species were hatched from the eggs in the 
spring of 1912 there are no data concernhig the complete life history 
or even of the way the larvae pass their first wmter. At the date of 
this wi'iting (Oct. 15, 1912), however, it seems quite evident that this 
year's wireworms will turn out next spring to be the ''small ones" 
which are always noted coming up to feed during February and 
March. 

At the time the beetles were being collected, in March, 1912, there 
was no vegetation of any kind in some of the fields, and the wire- 
worms, coming out from hibernation, were attracted to the old beet 
roots which are found in greater or less numbers in all of the fields. 
Nearly all larvae collected at this time, to the number of OA^er 3,000, 
were readily separable into two sizes. This has been reported before 
by other investigators.^ The smaller ones appeared to be about 
one- third grown, and very probably were the ones which had hatched 
the preceding spring, and were consequently about a year old. The 
larger ones showed more variation in size, occurring from three- 
fourths grown to practically mature. These larvae were probably 
1 and 2 years older than those of the smaller size. That there is 
a difference in age in the wireworms of this latter group is proved by 
the fact that of 100 isolated during March only 17 pupated in the 
period from July to September, and the remainder, some of which 
at the time of writing (December, 1912), had recently molted, had 
gone deep into the soil in the cages and seemed prepared to spend the 
winter. Now, from the fact that none of these large larvae could 
have come from eggs the preceding spring it seems very probable 
that this species will uphold the contentions of most of the American 
writers on this subject and spend three years in the larval state. To 
be exact, it would be a trifle over three years, as Prof. F. M. Webster ^ 
has pointed out, "the larvae hatching in the spring and pupating in 
the late summer." I^arvae have also been carried in the laboratory 
from Juno, 1910, to April, 1912, without pupatmg, so it seems evident 
that the larval stage could not be less than three years. 

1 Eleventh Report on the Noxious, Beneficial and other Insects of New York. By Asa Fitch, M. D., 1866. 

2 Underground Insect Destroyers of the Wheat Plant. By F. M. Webster. Bui. 46, Ohio Agr. Exp. Sta., 
1892. 



Bui. 123, Bureau of Entomjlogy, U. S. Dept. of Ag 



Plate IX. 




VA/oo^ OF qurAR-BEET WIREWORMS. YOUNG SUGAR-BEETS, SHOWING INJURY BY 
"^w'r^WORMS TO TAPH^oVs; ^ FEEDING MARKS VISIBLE ON END OF ROOTS. 



(Original.) 



Bui. 123, Bureaj of Entomology, U. S. Dept of Agriculture. 



Plate X. 




Work of the Sugar-Beet Wireworm. Nearly Mature Beets Killed 
by wireworms; blackened feeding marks noticeable on taproots. 
(Original.) 



123 Bureau of Entorrology, U- S. Dept. of Agriculture 



PLATE XI. 




Bui. 123, Bureau of Entomolog-y, U. S. Dept of Agncultur 



Plate XII. 



m 



'■?»^S, 



















j|. 123, Bureau of Entumology, U. S. Dept. of Agricultur. 



Plate XIII. 




3ij|. 123, 



Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate XI 




Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculturi 



Plate XV. 




LIFE HISTORY AND HABITS. 



25 



HABITS OF THE OLDER WIREWORMS. 



Wliile these wireworms were being collected in the fields there was 
a good opportunity to observe their feeding habits and theb" actions 
after emerging from hibernation. As the soil was wet to the surface 
by the intermittent rains, it was easy for the wireworms to reach the 
old beets which were scattered around on top of the ground. As 
the larvas had just 
emerged from hiber- 
nation they fed ex- 
tensively, %vith the 
result that whenever 
several wire wo r ms 
attacked a beet root 
it was soon honey- 
combed with their 
channels. Many of 
the wireworms noted 
were buried far more 
than their own length 
in the half-rotted 
beets. 

These larvae are 
carnivorous on occa- 
sions (see fig. 6), even 
under field conditions ; 




FlQ. (!.- 



A sugar-l)eet wireworm devouring one of its own kind; to illus- 
trate cannibalistic habit. (Original.) 



especially is this so 

during the earl}^ 

period when they are feeding most busily, and when at the same time 

they tend to be crowded. Under average field conditions, however, 

cannibalism is unimportant from an economic standpoint, as these 

larvfe are vegetable feeders l)v choice. 



LOCATION OF FOOD BY THE WIREWORMS. 



"Whether or not the wireworms, under field conditions, can locate 
food at a distance, and, if so, at what distance, is more or less problem- 
atical. Wlien wireworms were injuring l)eets in the fields it was 
found by careful digging that all which were near the beets were 
actually feeding on them. Wireworms noticed in fields containing 
young beets were almost always found in the beet rows, in spite of 
the fact that the ground there is compact and unfavorable for them. 
These facts seem to carry out the idea gained from the experiments 
with the young larvae, that they can locate food at a short distance, 
though this is not proven conclusively. 



26 THE SUGAR-BEET WIREWORM. 

ACTIVITY OF THE WIREWORMS. 

During the spring, when the soil is kept wet by the rains and loose 
by cultivation, it is probable that the wire worms are able to travel 
from one beet plant to another. Under laboratory conditions they 
have been noted to travel several inches daily, in the root cages, and 
the soil then is very apt to be compacted by wettmg. This point 
was tested by placing several ^^dI'eworms in a root cage without food 
in order to compel them to move. The soil, which was (|uite damp 
at first, was allowed to become pretty thoroughly dry, and then the 
cage w^as watered. The water followed the channels of the wire- 
worms, and in this way the wireworms could be easily traced by the 
wet streaks through the soil. These cages were 18 by 24 inches, yet 
in the week or 10 days the soil was drying out the wireworms had 
been able to channel all through the soil. Late in the summer, when 
the soil is more dry and compact, they move about much more 
slowly and are less anxious to feed, but as they do all theu- damage 
in the spring their actions at the latter time are of the utmost impor- 
tance. From all the observations on their activity it seems not only 
possible but even probable that one wireworm can destroy several 
young beet plants in a season. The sugar-beet plants are from 6 to 
8 inches apart in the rows. 

• 

WIREWORM INJURY TO BEETS. 

During the latter part of February and in March and April the 
ravages of the wireworms in the beet fields are very noticeable, 
especially so when the insects are present in numbers. In a year 
such as 1912, when their work w^as well scattered, injuiy can be 
noted, but it is possible to overlook it. 

Wlien the young beet plants are attacked they wilt, and upon 
examination the root is found to be either badly scarred or entirely 
severed, (PI. IX.) This injury generally takes place between 1 and 
4 inches below the surface. There are two general types of injury; 
in one the taproot is cut off clean, and the beet wilts and dies (see 
PI. X) ; in the other the wireworm, after eatmg into the root, turns 
and descends, eating off a side of the root as it goes down (see 
PI. IX). This, of course, scars the root badly, and if the beet is 
quite young and tender it is apt to die. If, however, the beet is 
quite strong and the root is swollen a little, so that the uijury does 
not cut off the sap supply, it will recover, though always remaining 
distorted and undersized. (See PI. XI.) 

In years when the wireworms appear in numbers they are likely 
to be concentrated in certain spots. Wlien this occurs they kill 
off all the beet plants in these areas, causing the characteristic 
"bald spots." (Pis. XII-XV.) Wlien once they have collected in 



LIFE HISTORY AND HABITS. 27 

this manner and have cleared off the heets it is almost impossible 
to raise beets there during that year, even if replantmg is resorted 
to several times, as the wireworms kill them as soon as they germinate. 

The injury caused by the wireworms is characteristic and should 
never be mistaken. In the first place, if the injury is recent, an 
examination will reveal the wireworm near by in the soil. If no 
wireworm is present an examination of the wound will readily show 
whether or not it is wireworm injury. The wound itself is stained 
black, as if rubbed with mk. Sometimes the black stam has pene- 
trated for a short distance into the sound beet tissue, but where it 
has not, it is considerably darker than the dry tissue surrounding an 
ordinary old wound. 

Effect of overjJ owing on the wireworm. — From the fact that wire- 
worm injury is often noticed in fields which have been overflowed 
in the latter part of the winter, it has naturally been supposed that 
overflowhig of the land is favorable to wireworms. This has not 
been proven to be entirely true. A careful watch was kept on the 
fields which are subject to overflow, and from these observations 
it seems that overflowing the land is of account only as it aftects 
the character of the soil and is theiefore secondary. In overflowed 
land which tends to be sandy the wireworms are likely to be destruc- 
tive year after year. On the other hand, flooded land which is a 
heavy silt and rich in humus is seldom so badly injured as is sandy 
unflooded land. One thmg has been noticetl, however, and that 
is that flooding the land does not seem to injure the insect in the 
least and therefore gives little promise as a control measure. Some 
of the beet fields which have sufi'ered the most during the last few 
years are those which almost every year are quite thoroughly flooded 
for two or three days. 

TIME THE WIKEWORMS CAN LIVE WITHOLTT FOOD. 

Whether or'not these larvae are able to find food m the soil is hard 
to determine, but judgmg from the length of time they are able to 
live without food it seems possible that they do receive some suste- 
nance from the soil, probably m the form of decaying vegetation. 
This is further borne out by the fact that where larvae are kept for 
a tune in a cage without food all the lumps of leaf mold disappear 
and the soil in the cage becomes homogeneous. 

Several observers have reported that these larvae can survive long 
periods without food, and one example which was noted in the 
laboratory will furnish added proof. Durmg June, 1910, Mr. H. M. 
Russell commenced a starvation experiment by placing several 
wireworms in a root cage, with ordinary soil, without food. In 
July, 1911, seven larvae were still alive and healthy. This cage was 



28 



THE SUGAR-BEET WIREWORM. 



watered regularly, except on two occasions, during the late summer 
of 1911 and was then allowed to become quite dry. As the larvae 
were killed by the drying soil they were removed so that they would 
not furnish food for the survivois. On September 12, 1911, the 
cage was again examined and only one larva was found alive. Two 
dead ones were found near the surface in the dry earth, and they 
had probably been killed by the drying out of the soil. This cage 
was then watered regularly and examined at intervals. The larva 
was still alive and active on April 15, 1912. During the latter 
part of April the cage, which was kept in the outdoor insectary, was 
blown over by the wind and broken. Before it was noticed the 
soil had dried out to such an extent that the larva was dead. An 



/ Kif>7/? 


/ yET^R 


3 MO. 


3 MO. 


3 MO. 


3 MO. 


3 MO. 


3 MO. 


3 MO. 


3 MO. 


/ 
















2 










3 










^ 










5 










6 










7 



























Fm. 7. — Diagram showing length of life of sugar-beet wireworm without food. (Original.) 

examination of the channels through the cage showed that the wire- 
worm had been quite active up to the time of its death. Wliile 
these larvae might have secured a little food during the earlier part 
of the experiment they could not have done so later, as they were 
checked up and removed when they died. In this experiment 
seven wireworms lived over a year without food, and one almost two 
years, as shown in the following diagram (fig. 7). 

These wireworms did not grow normally, for when the last one 
died after being in the cage two years it was less than half size. This 
larva should have pupated that fall, as it was at least a year old when 
the experiment began, and therefore should have been mature. 



LIFE HISTOEY AND HABITS. 29 

RELATION BETWEEN INJURY IN THE BEET FIELDS AND THE SIZE AND 
ABUNDANCE OF WIREWORMS. 

As is the case with practically every destructive insect, the greatest 
harm is done by the maturing larvae. It is therefore only a matter 
of watching the progress of injury in the beet fields to tell whether 
or not there are many mature wireworms, and whether, therefore, 
there will be an abundance of beetles the following year. In every 
year during wliich observations have been made thus far it has beo!^ 
a simple matter to foretell this point. In 1911 injury to the beets 
was quite heavy and general. From this it was reasonable to sup- 
pose that there were many mature wireworms in the soil and that 
the next year would see an abundance of beetles. Such proved to 
be exactly the case^ and beetles were quite common in the fields; 
so much so, in fact, that it was no extraordinary feat to collect over 
25,000 of them for the rearing work. In 1912, in the vicinity of 
Compton, the wireworm injury, while quite general, was light, and 
using the same reasoning it was probable that there would be few 
beetles in the spring of 1913. This has been partially proven by the 
fact that very few of the larvae taken in the fields during 1912 pupated 
the same fall. The 300 wireworms collected in the summer of 1911 
produced almost as many pupa3 in the fall of that year as the 12,000 
wireworms collected in the summer of 1912 produced during the 
succeeding fall. 

MOLTING OF THE WIREWORMS. 

The wireworms molt in their channels, and wriggUng from their 
old skin (PI. Ill) they He stiU for some time until their new sldn has 
hardened. If the channel is larger in cross section at the place 
where the wireworms molt, it is so Uttle larger as to be almost unno- 
ticed. When ready to molt the larvae Ue still for some time, in cer- 
tain cases for several days, before the skin splits and they are able 
to free themselves. In a majority of the cast skins noted the skin 
had split down the dorsum of the thorax. Where tliis occurs the 
process of molting is simple and seldom takes more than two or 
three hours. The cast skin is also in one piece. Now and then the 
skin splits irregularly, and in these cases the molting process requires 
more time, sometimes several days. In one case noted the wireworm 
shed the skin from its head a fuU week after it had molted on its 
thorax and abdomen. In such cases the skin is quite apt to be torn 
into several pieces and is almost useless for study. 

Directly after molting the wireworm, with the exception of its 
mandibles, is a rather shiny opaque white. The mandibles are yel- 
lowish, shading to brown at the tips. The mreworms color quite well 
in from one to three days, but they often remain quiescent for weeks 



30 THE SUGAR-BEET WIREWORM. 

after molting. This is especially apt to be the case in the fall, when 
they are sluggish. 

Most of the larvae observed during 1912 molted twice. A few 
were seen to molt once, although it is possible that a molt might have 
been overlooked in a few instances. In the case of a few others it 
was thought that a third molt was seen, but this is doubtful. From 
tliis it is impossible to give even the approximate number of molts 
with an}" degree of accuracy, but present indications are that they 
molt at least five or six times. 

The Pupa. 

pupation. 

In about July or August the mature larvfe become shorter, and 
while they are not more constricted between the segments, they have 
the appearance of being so, as the segments swell sUghtly in the middle. 
At the same time there is a sUght change in color, the entire larva 
appearing sickly and of a dirty yellow color. During tliis period 
the wireworms lose most of their activity, and whatever m.ovements 
they make are slow and weak. When pupation is only a short time 
off they are quite hel])less, and if their pupal cells are broken open 
they are unable to make new ones. Several which were taken in this 
condition were able to pupate safely, the operation taking place in 
a Janet ants-nest cage. 

THE PUPAL CELL. 

The pupal cell is sim})ly an enlargement at the end of the larval 
channel, and is slightly elUptical in shape. It is unlined but is 
quite smooth and the soil is weU compacted. The depth of the pupal 
cell below the surface varies between 4^ and 9 inches, but most of 
those observed were at a depth of about 6 inches. It is apparent 
that the wireworms move very little preparatory to pupating, as 
pupae are often dug up with the wireworms close to the old beet 
roots. 

SOIL CONDITIONS AFFECTING PUPATION. 

The pu})* (PI. V) are unaffected by a little dryness, but if the soil 
becomes quite dry for a long ])eriod they do not emerge. Many 
healthy pupie were dug up in the field in soil wliich contained only 
a little moisture. Those which came through best under laboratory 
conditions were from cages where the soil was kept only moderately 
damp. Where the soil was too wet a large percentage of the pupae 
sickened and died. Those found dead under these conditions were 
attacked either by a fungus or a bacterium, or sometimes by both. It 
was not determined whether these organisms were parasitic or sapro- 



LIFE HISTORY AND HABITS. 31 

phytic. An attempt was made to rear some of the pupa? in the plas- 
ter-of-Paris cages, but the cages seemed to be too damp, and all the 
pupa? died. These appeared like those killed in the flooded cages, 
and the same bacterium and fungus infested them. 

VITALITY OF THE PUPA. 

The pupal stage is the most unprotected state in the life cycle of 
this insect, and is the one wherein the insect is most liable to mechan- 
ical injury. A small percentage of the pupae dug up out of doors 
were injured when their pupal cells were broken open, and conse- 
quently died. On the whole, however, the pupa is not nearly so 
susceptible to injury as is the popular belief. Such pu})£e as were 
unearthed in the field were kept under artificial conditions and 
handled quite roughly and often, yet most of them produced adults. 
The two pupae which were photographed for this bulletin (see PL V) 
were handled several times with forceps, were exposed on a glass plate 
to light and temperature for hours, and on one occasion were dropped 
from the table to a chair, a distance of about 10 inches. In spite of 
this treatment both produced normal adults, and when last observed, 
October 14, 1912, were alive. There were several similar cases in 
which the results were the same as in the example cited. The pupae 
are quite helpless and are unable to make new pupal cells in case the 
old ones are destroyed. For this reason, i)robably, a large per- 
centage of those disturbed in the field die from exposure. The pupae 
are sensitive to light, heat, and contact, and when disturbed move 
their abdomens in such a way that the tip describes a circle. As 
the pupa becomes older it becomes more deeply colored and more 
sensitive and active. 

CHANGES IN COLOR OF THE PUPA. 

The first signs of coloration of the pupa are the eyes, and these 
appear as dusky bluish spots. The abdomen and thorax then be- 
come slightly yellow and the mouthparts and wing covers very 
faintly dusky. The tip of the abdomen remains whitish. About a 
week before emergence the entire pupa becomes darker, and just a 
few days before emergence the. wing covers and mouthparts are 
quite dusky and the eyes assume a dusky color, the mouthparts, 
cyoH, and wing covers remaining a little the darkest and being quite 
conspicuous. 

LENGTH OF THE PUPAL STAGE. 

The length of the pupal stage under laboratory conditions varied 
from 25 to 36 days, with most of the adults emerging in about 26 
to 32 days. These were kept as nearly as possible under conditions 
which would compare favorably with field conditions. This gives, 
roughly, a period of a month for the pupal state. 



32 the sugae-beet wireworm. 

The Adult, 
emergence of the adult. 

During the last few days before emergence the pupa becomes very 

sensitive to hght or contact, and when disturbed turns around in its 
pupal cell by moving its abdomen. An attempt was made to photo- 
graph one during this state, but in the hour and a half it was exposed 
it did not remain quiet long enough for an exposure to be made. 
The abdomen is drawn in and out as if the beetle were tiyiug to break 
the pupal skin. This goes on for some time, often for more than a 
da}^, and finally the pupal skin splits down the dorsum of the thorax 
and is worked off. The beetle (PL XVI), which has been quite active 
in shedding its skin, now becomes quiescent, and folding its legs and 
antennae as they were in the pupa, remains in the pupal cell. The 
cast pupal skin lies in the posterior end of the pupal cell along with 
the last larval skin, and helps form an obstruction between the pupal 
cell and the old larval channel. The cast pupal skin is semitrans- 
lucent white and thin, but at the same time quite tough. 

In two cases the legs of the beetle broke through the leg cases 
before the pupal integument split down the dorsum. Neither of 
these adults completely emerged, and after moving their legs feebly 
for a few days they died. 

PERIOD OF EMERGENCE. 

The period of emergence of the beetle from the pupa varies widely. 
This was tinje both of those which were reared in the laboratoiy and 
of those pupse which were collected outdoors. Adults emerged be- 
tween early August and October in the laboratory, and pupas from 
the fields have given adults between the same dates. One pupa 
from the field transformed to adult October 6. Mr. Russell observed 
one adult emerge in the laboratory as late as October 17. 

Beetles disturbed during the fall are able to bury themselves and 
live if they are not injured. Several which emerged in the laboratoiy 
were constantly disturbed so they could be watched, but it seemed to 
have no ill effects on them. 

ACTIONS DIRECTLY AFTER EMERGENCE. 

As soon as the pupal skin is shed the adult, retaining the position 
it had held as a pupa, lies in the pupal cell. At first the beetle is a 
little softer and lighter in color, but soon becomes hard and fully 
colored. Smce none of the pubescence on its thorax or elytra has 
been rubbed off, it appears grayish in color. At this time these 
beetles are totally different in their actions than they are in the 
spring, when they appear on the surface, being negatively heliotropic 
and hiding under anything they can find or burrowing into the soil 
when exposed to light. They also seek damp, cool quarters in 



Bui 123, Bureau of Entomology, U. S. Dep1. of Agriculture. 



Plate XVI. 




31U 
o 

z I-' 

£ S5 

§^ 

o > 
l_i 

_i < 

■^ IT 

hi i- 



ID 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agncultur 



Plate XVII. 



■' jf-!f.'*v^^%^ - :r^ff^ \ 




I 



Fig. 1.— Beetles of the Sugar-Beet Wireworm (Limonius californicusi in 
Secondary Hibernation Under Slice of Sugar Beet. (Original.) 




Fig. 2.— Beetles OF the Sugar-Beet Wireworm Photographed while Feed- 
ing on Slices of Sugar Beet. (Original.! 



HABITS OF THE BEETLES OF THE SUGAR-BEET WIREWORM 
(LIMONIUS CALIFORNICUSl. 



LIFE HISTORY AND HABITS. 33 

preference to the dry, warmer ones. The habit of feignmg death, 
so marked in the spring when they aj)pear, is totaUy hicking at this 
time, and about the only way to make them move is to touch them. 
When they are dug up from their pupal cells, or from the ground 
in which they have been hiding, they become active in a short time, 
look for another hiding place, and as soon as they find it draw in 
their legs and antennas and resume hibernation. They are very 
sluggish, move slowly, and do not attempt flight. 

APPEARANCE OF BEETLES IN THE SPRING. 

In the early sj)ring, during a period which covers two months, 
the beetles dig out of their cells, appear at the surface of the ground, 
and become partially active. That the time of this "emergence" 
is governed by several factors is strongly suggested by the diversity 
in the time of appearance. The average mean temperature is prob- 
ably the main factor, but such causes as the kind and porosity of 
the soil in which they have pupated, and the rains, certainly help in 
determining the time of their appearance. This latter point w^as sug- 
gested by the fact that beetles were always more abundant in the 
fields following a rain than they w^ere directly preceding it. This 
might be explained by the fact that their cells became too wet and 
they had to dig out for safety. 

Just after their app(uirance in the spring the beetles are very 
sluggish and collect under rubbish of all kinds in the field. They 
still appear to be in a state of semihibernation and none are ever 
noted sunning themselves, feeding, or mo^dng about. Wlien their 
shelters are removed they are found in the same position they main- 
tain during hibernation, with their legs and antennas folded closely 
against then* bodies. When the sunhght strikes them they slowly 
become active and search for another hiding place. In every respect 
their condition at this time resembles hibernation, except that they 
more quickly become active. To distinguish between this condi- 
tion and their true hibernation in the soil, tht^ former for want of a 
better word was called ''secondary hibernation." This period lasted 
from about the middle of February, or a little earlier, till the middle 
of March. It is little more than a transition period between their 
hibernation and their period of activity. During this time the 
weather was quite cold, with cloudiness and showers at intervals. 

BEGINNING OF THE PERIOD OF ACTIVITY. 

The beetles are so slow to show signs of activity and so sluggish 

during the earlier part of their active period that no hard and fast 

line can be drawn between the latter and their so-called secondary 

hibernation. Furthermore, under every beet active and inactive 

6140°— Bull. 123—14 3 



34 THE SUGAK-BEET WIREWORM. 

beetles may be found side by side. Now and then, about the middle 
or latter part of April, a beetle is seen sunning itself at the edge of 
a beet under which it had been hiding. At about this time, also, it 
was noted that the underside of many of the beets which sheltered 
beetles was roughened and had the appearance of being shredded. At 
first no attention was paid to this until by chance a beetle was noted 
feeding on an old beet, and then it was seen that the roughened 
places on the beet were the feeding marks of the adults. Whenever 
a beet was turned over the beetles were for the most part active 
(PI. XVII, fig. 2), but a few were still in then* secondary hibernation 
(PI. XVII, fig. 1). The feeding marks on the beets become more 
and more noticeable but are never especially extensive, as the adults 
at the period of their greatest activity are light feeders. 

Even at this time the beetles are not entirely normal in their 
actions. This is most noticeable in regard to the habit of feigning 
death, so characteristic of most of the elaterids. ^Mien a group is 
exposed by removing the beet under which they have been hiding, 
at least half of them move about searching for shelter. This is 
probably due to the fact that their senses are not very acute at this 
time, and they consider only shelter. About a month later, however, 
when a gToup of beetles is exposed by removing the beet shelter, 
most of them remain quiet for some time, even though they may 
happen to be in an unusual position. 

VARIATION IN THE SIZE OF BEETLES. 

Among the beetles taken in the field there was a very noticeable 
variation in size. (See PI. I.) The length was often found to vary 
between 9 and 12.2 mm., and the width between 2,5 and 3.5 mm. 
The larger ones outnumbered the smaller ones ahnost 2 to 1, since 
about 15,000 of those collected could be referred to the larger size 
to about 9,000 of the smaller, while about 2,000 or 3,000 were so 
nearly on the dividing line between the other two sizes that they 
were unclassified. At first the large ones were thought to be females 
and the smaU ones males, so it was concluded that the females out- 
numbered the males about 2 to 1 . Such did not prove to be entirely 
the case, for when copulation became general some of the small ones 
proved to be females, and not a few of the larger ones were seen to 
be males. Everything considered, it seems that sex is quite inde- 
pendent of size, for the males and females were seen to occur in about 
equal numbers. 

VARIATION IN THE COLOR OF BEETLES. 

From the outset it was noted that there was great variation in 
the color of the beetles. This difference was most noticeable on the 
elytra, which varied from light buft' to deep brown or dusky black. 



LIFE HISTORY AND HABITS. 35 

There seemed to be a rather plain dividing hne between those with 
the buff wing covers and those with the brown ones, so they were 
separated. About 1,500 or 2,000 could be referred to the former 
class. Some of these were sent to Dr. Chittenden for determination, 
and concerning them he wrote as follows: 

No. 495 (?) is Limonius sp. near californicus. It doeK not appear to agree perfectly 
with the californicus with which I have compared it, and is not represented in our 
duplicate collection. 

The relationship of these beetles will be worked out in the future. 

The true adults of Limonius californicus also varied considerably 
in color, as some were found which were a relatively light brown. 
These color variations occurred in all sizes and both sexes, so color 
seems to have no bearing on the sex of the adult. 

FEEDING OF THE ADULTS, AND FOOD PLANTS. 

When the beetles were first collected the character of their food 
was unknown, and in an endeavor to find their natural food all the 
different kinds of foliage found in the beet fields were tried, but with- 
out success. Adults by the hundreds were placed in cages contain- 
ing tender young beet plants, and while they climbed all over the 
plants they were never seen to feed on them, nor could any feeding 
marks be found on the plants. A close watch was kept on the 
adults collected in the field, and at last, as has been stated before, 
they were noted feeding on the old left-over beet roots, now half 
dried and partially rotten. When these were substituted for the 
beet foHage in cages, feeding was begun at once. A few instances 
were noted where the adults had eaten into the roots to such an 
extent that the head and thorax were hidden. Such cases, how- 
ever, were rather exceptional, and the beetles may be considered as 
fight feeders. In addition to this, their feeding, from an economic 
point of view, may be disregarded. 

The adult has been noted feeding on the following substances: 

Old beet roots. 

Alfalfa roots ( Medicago sp.). 

Johnson-grass roots {Sorghum halepense). 

Wild beet roots (Beta sp.). 

Young beet roots. 

The old beet roots are the favorite food, and it is only occasionally 
that beetles are noted feeding on the other substances fisted. 

The beetles seem to be able to locate food readily and at quite a 
distance. In the laboratory whenever a sfice of beet was placed in 
the cages the adults would be clustered about it in a very short time. 

In the field the beetles were always found at the old beets and 
always occurred in the greatest numbers where the beets were most 
plentiful. 



36 



THE SUGAR-BEET WIREWORM. 



Ill one field, which liad a great many old l)eets on the surface, the 
beetles were taken from under almost every one, and sometimes in 
large numbers. It was a common matter to find from 30 to 70 
adults under single beets, and as many as 243 have been found hiding 
under one beet. Another favorite shelter was afforded by the old 
beet tops (PI. XVIII) left in the field from the previous year's harvest. 
In the field which adjoined this one there were few or no old beet 
tops and beets for shelter, and here beetles were rarities. This field, 
just the year before, suffered more than any of the surrounding fields 

from wireworm in- 
jury, so there must 
have been beetles 
which developed from 
the m a t u r e w i r e - 
worms that had 
caused the damage. 
In other fields, how- 
ever, which had suf- 
fered similar injury 
but in which the old 
beets had been al- 
lowed to remain, 
beetles were present 
in large numbers. 
There seems to be 
only one explanation 
for this fact, and that 
is that the adults had 
emerged from the 
cleaned fields and, not 
finding any shelter, 
had been obliged to 
move to other fields 
or be destroyed by 
the birds. This was further indicated by the fact that all the beetles 
found in the clean fields were moving about. The state of affairs 
was found to be the same in other fields aggregating over 600 acres, 
where the conditions were similar. 




Fig. S. — Screen cage used in observing oviposition of adults of the 
sugar-beet wireworm under field conditions. (Original.) 



STYLES OF REARING CAGES USED. 



Several styles of rearing cages were used, but only a few will be 
considered. The ones used indoors consisted of battery jars, flower- 
pots, and flowerpots with lantern globes. The highest death rate 
was found in the first, because there was no drainage and the contents 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. 



Plate XVII 




Secondary Hibernation of the Sugar-Beet Wireworm (Limonius cali- 
FORNicusi. Beet Tops Used by Beetles as Quarters for Secondary 
Hibernation. (Original.) 



LIFE HISTORY AND HABITS. 37 

tended to become foul. The two types last mentioned were about 
equal in efficiency, but the main difficulty lay in the fact that they 
were small and it was easy to overcrowd them. 

The cage used most successfully was a large screen cage of the 
connnon type, kept outdoors. (See fig. S.) Within the cage were 
several flowerpots, buried to the level of the ground, each containing 
young beet plants. The soil in the pots was kept loose and damp, 
and the soil around the flowerpots was tamped hard. This cage was 
large, well ventilated, and gave the beetles plenty of room in which 
to fly about. Its best feature lay in the fact that the beetles all de- 
posited their eggs in the flowerpots, since this was the only place 
where they could bury themselves easily. It this way the eggs were 
concentrated much more than they would have been under natural 
circumstances. As soon as one flowerpot contained a great many 
eggs it could be removed and another substituted. This cage also 
gave natural conditions, as the soil it contained was just as damp as 
that in the field, and since the cage was placed in the sun and was so 
airy the beetles were always kept at the field temperature. The 
death rate was very much lower in this cage than in any of the others 
and there were live adults in it for some time after all had disappeared 
in the other cages. 

DURATION OF LIFE UNDER VARYING CONDITIONS. 

To test the duration of life under varying conditions some adults 
were placed in various styles of cages and others were kept under 
various conditions as concerned the food and water supply. Some 
were kept without either food or water, some with food but %vithout 
water, and some with water but without food. In every instance 
the beetles lived much longer than was expected of them and proved 
that they are not onl}^ quite hardy but can get along on little food. 

One hundred and forty adults were placed in dry battery jars 
without food or water, and the jars were closed with gauze. The 
results were as follows : 

Eighty-two adults died in from 9 to 12 days. 
Forty adults died in from 12 to 14 days. 
Eleven adults died in from 14 to 16 days. 
Five adults died in from 16 to 18 days. 
One adult lived 20 days. 
One adult lived 22 days. 

None of the beetles was very active after the twelfth day. These 
conditions were much more severe than any that they might encoun- 
ter under field conditions. 

The adults kept with water but without food were also kept in 
battery jars. These jars contained about 3 inches of soil, and this 



38 THE SUGAB-BEET WIBEWOEM. 

soil was kept quite damp by additions of water from time to time. 
This cage presented very much the condition which would hold 
in the field if all the food could be eliminated. Five hunch'od 
and sixty beetles were used in this experiment, with the following 
results : 

About 60 died before 10 days. 
About 100 died before 10-15 days. 
About 200 died before 15-18 days. 
About ]00 died before 18-22 days. 
About GO died before 22-25 days. 
About ."^O died before 25-28 days. 
About 6 died before 28-30 days. 
About 2 died before 30-31 days. 
About 1 lived for 34 days. 
One lived for 40 days. 

The last 10 to die were females. Their abdomens were quite 
swollen, but they did not lay any eggs — at least none could be 
found — and when they were dissected after death the ovaries, while 
containmg some eggs almost mature, were quite shrunken and dry. 
None of the beetles was very active after 15 days, and after 25 days 
they were very feeble, the last few to die being unable to walk during 
the last days they lived. 

Many adults were separated and kept in vials and given food but 
no water. Care was exercised to have this food as dry as possible. 
Out of 78 used in this experiment only 12 died during the first 15 
days, and the remainder were quite active. It was so difficult to 
obtain the food dry enough to affect them that the experiment was 
discontinued. 

LENGTH OF TIME ADULTS CAN BE SUBMERGED. 

Several adults were submerged in water in a tube and kept below 
the surface by a smaller tube placed within the first one. The 
water was perfectly clear and care was taken to remove all the air. 
At the end of 15 minutes the beetles had ceased to move and at the 
end of 20 minutes they were removed. They seemed dead, but within 
a few minutes were moving about actively and seemed none the worse 
for their treatment. 

Another lot was submerged for 40 minutes and within a half hour 
after being taken out were as active as ever. The tests were not 
carried further, as these were considered as severe as any they would 
be subjected to under field conditions. Twenty adults were floated 
on water for 15 hours and at the end of that time only three were 
dead. From these results it was concluded that a majorit}'^ of tlie 
beetles could survive a severe storm. 



LIFE HISTORY AND HABITS. 39 

EFFECT OF TEMPERATURE ON THE ADULTS. 

The adults of many of tJie eastern species Lave been reported by 
some observers as being primarily nocturnal in habits.^ Other 
observers record them as flying readily both by day and night. The 
adults of Limonius californicus seem without exception to be warm- 
weather insects. They not only attain their greatest activity 
during the middle of the day when the heat and light are at the 
maxhnum, but during the morning and evening hours they are 
sluggish and quiet. Some specimens were kept in the WTiter's 
room during their entire life and none was ever observed feeding or 
copulating at night . On the warmest nights a very few were observed 
moving about sluggishly, but their activity at this time can not be 
compared to that which occurred during the daytime and especially 
when the temperature was over 75° F. 

Several experiments were conducted for determmiiig the direct 
relation between temperature and activity. The apparatus used 
was very similar to that used in the boll weevil investigations,^ 
except that instead of the outer tube a flask was used, as it was believed 
that this would afford more even heating. 

The results agreed quite closely with those recorded in Bulletin 
No. 51 (pp. 101-102) and an approximation is given below: 

48° F. Beetles quiescent. 

54° F. Few crawling about sluggishly. 

60° F. Beetles all moving about. 

70° F. Beetles becoming active. 

75° F. More active, few flying. 

80° F. Many flying. 

85°-90° F. All flying, very active, seem greatly excited. 

93°-94° F. Period of greatest activity. 

97° F. Few becoming quieter. Seem to be suffering. 

99° F. Many becoming quieter. 

This experiment was varied slightly by placing damp filter paper 
in the inner tube so that the heat would not be so dry. The new 
results did not differ very startlingly from the preceding, except 
that the beetles did not seem to suffer so much at the higher tempera- 
ture and seemed less excited. 

Under field conditions 75° to 80° F. seems to be the optimum 
temperature for their various activities. At 70° F. they are quite 
active, but few are noted in flight, especially if there is a moderate 
wind blowing. At 60° F. very few are noted moving in the fields, 
and these are generally close around the beets under which they have 
been hiding. The beetles are always more active on bright days 
than on darker days, even if the temperature is the same. This 

1 Comstock and Slingerland, Bui. 33, Cornell Agr. Exp. Sta., 1891. 
a Bui. 51, Bur. Ent., U. S. Dept. Agr., PI. XVI, fig. 72, 1905. 



40 THE SUGAR-BEET WIREWORM. 

dijfference in tlieii- actions caused by liglit was very noticeable when 
cages were removed from the insectary and phiced in the sunlight. 
The beetles would fly about at once and before long many pairs 
could be taken in copulation. Wlien the cages were replaced in the 
insectary activity would cease as suddenly as it had begun. 

ABILITY OF THE ADULTS TO WITHSTAND UNFAVORABLE CONDITIONS. 

The adults showed remarkable ability to withstand shocks of 
various kinds, whether occasioned by physical injury or by sudden 
and unfavorable climatic conditions. 

A few cases noted in the field will show their ability to withstand 
physical injury. When beetles were collected in the fields individuals 
were noted on several occasions to have been injured by their pre- 
daceous enemies, Calosoma cancellatuni Esch. and C. semilseve Lee, 
and these were separated from the others so they could be watched. 
Those which had merely lost some of their legs did not seem to be in 
the least inconvenienced. Others which were quite severely injured 
managed to survive as long as most of the other beetles. One, which 
had its abdomen so nearly severed near the anterior end that it had 
lost one of its elytra, lived for several days. 

As to their ability to withstand unfavorable weather conditions, 
it may be stated that while over 25,000 beetles were collected from 
the field in a period which exceeded a month, very few were found 
dead. During this period there were sudden and great changes in 
temperature and several severe rainstorms. 

In view of the fact that the beetles seem to be so hardy in the field, 
it is difficult to explain the heavy death rate which was noted in all 
the cages about the time of oviposition. It seems that they must 
lose much of their vitality durmg their later life, so that by the time 
oviposition is about to take place they are comparatively weak. 

METHOD AND TIME OF MATING. 

Wlien once the adults have attained their normal activity they 
mate readily during the warmer hours of mild days. Beetles were 
taken mating as early as March 17, 1912, and as late as April 23, 1912. 
Every pair taken in copulation in the field was taken between 9.30 
a. m. and 3 p. m. No pairs were ever found in copulation if there 
was a strong wind blowing or if the sky was cloudy or the weather 
cold and rough. The mated pairs were generally found near or 
beneath the beets under which they had been hiding and feeding, 
though one pair was found in a crack in the soil, about 2 inches below 
the surface. 

Temperature has a very direct effect on copulation, as was ])roved 
by the laboratory experiments. Battery-jar cages, when taken from 



LIFE HISTORY AiSiD HABITS. 41 

the cold rooms, coiitained only semidormant beetles, but alter being 
placed in the sun for a time the beetles very soon became active and 
copulation took place. When the cages were returned to the cold 
rooms it was only a few moments until copulation ceased and the 
beetles became sluggish again. 

The method of matmg of these beetles seems to be more or less 
unique. The male shows no signs of excitement until he conies in 
contact with the female, and then he rapidly attempts copulation. 
After the male has assumed his position he throws himself over back- 
ward so that he is on his back wdth his body in the same line with 
that of the female, but pointing in the opposite direction. The 
male then folds his legs and antennae close against his body and 
remains quiescent during the operation. It disturbed the female 
seeks shelter, walking slowly and draggmg the male after her. The 
duration of the process varied greatly in the cases noted, covering 
from 7 to 19 minutes. After the operation the male was generally 
noted to be much more active than the female, but was not seen to 
attempt copulation a second time, even where the pair were coniiiied 
in a small vial for some hours. 

Much of the copulation attempted in the cages was unsuccessful, 
about nine attempts out of every ten commg under this head. When- 
ever several males were attempting copulation with tlie same female 
at the same time they were noted to fight one another. 

About April 1, 1912, the abdomens of the females began to swell 
noticeably and a close watch was kept for the eggs. Every day 
about six females were dissected so that the development of the eggs 
could be watched. The immature eggs were small and disk-shaped, 
being little more than half as large as the mature eggs. They ap- 
peared as opaque spots in the translucent jellylike ovaries, which 
filled quite completely the ventral portion of the abdomen. The 
development of the eggs was relatively slow, the greatest change 
appearing in the ovaries, which increased rapidly in size until at 
the time of oviposit ion they practically filled the abdomen. 

ACTIONS OF THE ADULTS AFTER MATING. 

During the last week before oviposition the females spent all their 
time burrowing under the soil, and were never noted feeding or on 
the surface. Whenever they were dug up they immediately buried 
themselves again. If the ground was not allowed to dry out too 
much the females remamed active and healthy, but in several cells 
in which the soU completely dried out the females died. 

The males did nothing but feed and crawl about on the surface. 
They lived, on the average, from two to four weeks after mating, so 
it seems possible that one male might fertilize more than one female. 



42 THE SUGAR-BEET WIREWORM. 

In one instance, when the female in a cell had been dug up she came 
in contact with the male. The latter attempted copulation, but 
unsuccessfully. 

OVIPOSITION. 

On April 9, 1912, the first eggs were deposited. These were laid 
in a vial which contained several females in which the development 
of tho eggs was more advanced. These eggs were scattered through- 
out the soil. 

In only one instance was a female noted in oviposition, antl that 
was under unnatural circumstances. Several gravid females had 
been placed in a glass, on the bottom of which was about half an inch 
of very compact soil. This glass was placed in the dark room for 
several hours, and when observed again one female was attemptmg 
oviposition between the soil and the glass. The beetle thrust her 
ovipositor do^vn several times, and finally the egg was placed in the 
bottom of the hole made by the ovipositor. The ovipositor was 
then withdrawn slowly and then thrust back part way several times 
as if the beetle were trying to cover the egg. The entire operation 
took but a very short tune. 

Wlien the soil in the cages was broken up and examined for eggs 
it was seen that oviposition under natural conditions must be quite 
similar to that observed, as eggs were found at intervals under the 
channel made by the digging female. 

By the latter part of May the females became very scarce, as they 
live but a short time after layuig their eggs. The males for the 
greater part died during about the middle of the period of ovipositioii. 

Approximate Length of the Life Cycle. 

Considermg the length of the egg stage as one month and the 
length of the pupal stage as the same, these, added to the length of 
the life of the adult, will give from five to eight months. If, as has 
been stated before, the larval stage lasts for over three years, it is 
seen that the length of the life cycle from egg to egg would be four 
years. 

SEASONAL HISTORY. 

Beetles from Emergence to Hibernation. 

The life of the adult, from emergence, through hibernation, until 
their appearance after hibernation, is governed to a great extent by 
conditions over which the beetles themselves have no control. The 
greater part of the beetles emerge from the pupae about the middle 
of September. The beets are plowed up for the most part during 
September and October, so the insect is in danger of being disturbed 
either during the pupal stage or soon after it has changed to the 



SEASONAL HISTORY. , 43 

adult. The plowing which the land receives at this time can hardly 
be called a plowing, but the ground is torn up to a depth of from 6 
to 12 inches. As the soil is dry, that disturbed is for the most part 
in large clods, so there is little chance that many pupae or adults 
will be disturbed. 

Those which by chance are disturbed are either killed outright or 
have to live under changed conditions until spring. If they happen 
to be pupae the chances must be very much against them, and they 
will probably either be injured by the sharp particles of dirt or will 
dry out. If the insects are in the adult stage they will have a better 
chance of survival, but here also they may be compacted into the 
soil and killed, or be eaten by birds, since, living under unnatural 
conditions, they are obliged to appear earlier in the spring than they 
would othermse. Even when kept under laboratory conditions 
many of those disturbed in the fall can not live till the normal time 
of their appearance. 

Hibernation. 

The adults pass the severest part of the winter in the soil. If 
disturbed they winter in their pupal cells, where they are well pro- 
tected, as these are on the average about 6 inches below the surface. 
This tempers the winter for them very well, and moisture can reach 
them only after heavy rains, and these seldom if ever occur except 
at the latter part of the hibernating period. When the beetles are 
disturbed in the fall they dig down into the soil for shelter. The 
depth to which they go varies. In some cases, where the soil is 
powdery, they go down only about from H to 3 inches, but when 
the soil is partially made up of clods and full of cracks they are 
sometimes found from 4 to 6 inches below the surface. 

Mortality During Hibernation. 

Under ordinary circumstances and where the pupal cells are undis- 
turbed, a large percentage of the beetles emerge safely — at least this 
is so under laboratory conditions. One cage was watered and kept 
outdoors so that the beetles were subjected to conditions as severe 
as the ordinary field conditions, yet all came through safely. Of 
those disturbed in the fall, not enough have been tested to give 
representative figures, but thus far almost a third of those treated 
in this way have died during hibernation. 

Gradual Emergence from Hibernation. 

The time of the appearance of the beetles in the spring is influenced 
to a large extent by artificial agencies, the most important of which 
is spring plomng. This plowing, which takes place as soon as possible 



44 



THE SUGAR-BEET WIREWORM. 



after the first rains, is quite thorough, averaging from 10 to 14 inches 
deep, and as the soil is damp and mellow at this time very few clods 
are left. This treatment disturbs most of the beetles*, and these, 
unless the weather is too severe, ma}' come to the surface and finish 
their hibernation in any sheltered place they can find. If the weather 
is severe and cold many of the beetles prefer to remain in the soil. 
It is due to these conditions that there is a variatit)n in the time of 
appearance of the adults, as has been proven by systematic collec- 
tion in the fields. 

Collections were made in some of the fields day after day and 
tabulated. The beets which sheltered adults every day were marked, 
and the beetles which were collected from them every day were 
noted. The following table gives the number of beetles which were 
taken from under the same beet on the dates given: 

Table I. — Emergence of adults of the sugnr-beet ir ire iron n from hibernation in the field. 



Date. 


Number of 
Ijeetles. 


Date. 


Numlier of 
beetles. 


Feb 29 


2 

i 

7 

3 

17 

2 

1 

1 



29 

47 

13 


Mar. 12 

Mar. 13 

Mar.l4 

Mar. 15 

Mar. Ki 

Mar. 17 

Mar. IS 

Mar. 19 


4 


Mar. 1 

Mar. 2 


7 
1 


Mar. 3 

Mar. 4 . . . 


3 


Mar.5 

Mar.G 


11 




Mar. 8 

Mar. 9 


Mar. 23 

Mar. 24 

Mar. 21) 


1 

3(1 


Mar. 1(1 

Mar. 11.. 


9 



As these notes were t;iken before tlie beetles were moving through 
the field very generally, it appears that the latter must have come 
from the soil near the beets which were used for hibernating quarters. 

Secondary Hibernation. 



The beetles which are driven to the surface prematurely seek what 
may be termed "seccmdary hibernation" under almost any shelter 
wliich can be found. The substances in the following hst, under 
which beetles were found, are named in about the order of prefer- 
ence : 



(1) Left-over beets. 

(2) Old beet tops. 

(3) Wild beet roots. 

(4) Alfalfa roots. 

(o) Johnson j^rass roots (Sorghum hale- 
pense) . 

(6) Lanil)8(]uart('rs {('he'no podium sp.'). 

(7) Pigweed stalks ( Aimiranthu.s refro- 
flexus) . 



(8) Wood. 

(9) Clods. 

(10) Cracks in soil. 

(11) Old sacks. 

(12) Manure. 

(iS) Miscellaneous rubbish. 



SEASONAL HISTORY. 45 

Iteuis 8 and 9 (wood and clods) sheltered practically aU the beetles. 
The last-named item included paraffin roofing, old bottles, pottery, 
etc. The wide diversity t)f this hst shows that the beetles are not 
very particular about the character of their shelter. 

It is interesting at this time to note that no beetles were taken 
from under charred beets or wood ashes. This point w^as well illus- 
trated in the corner of one of the fields which proved to be the choicest 
collecting ground. It happened that in this place a large amount 
of rubbish had been burned the pre\dous year, and about half the old 
beets lying about on the ground were charred. Adults were taken 
in numbers from this corner daily, but not one was ever found under 
the beets which were charred. The same thing was true of the wood 
ashes. 

The numbers of beetles taken from single beets were much larger 
than might have been expected. As has been stated before, as many 
as 243 have been taken from under a single beet, and on one occa- 
sion 187 were taken from under a single beet top which was less than 
3 inches in diameter. The concave top was entirely filled with the 
beetles, which in some places were piled from 2 to 4 deep. 

Occurrence of Beetles in the Field. 

Up to the middle of March the adidts are found close to their 
hibernating c^uarters, either feeding cr suiuiing themselves. At about 
tills time, however, there is a general dispersal cl beetles, and their 
collection becomes a difficult matter. Flight is of common occur- 
rence, as is copulation. The writer watched many beetles which 
were moving about the fields, to see what they were doing, but to 
all appearances they did nothing except wander about. Some were 
watched to see if they would oviposit, but nothing of this kind was 
noted.^ To judge from their actions in the laboratory cages, these 
adults were moving about preparatory to binrowing into the soil for 
oviposition. 

Effect of Food in the Field on Dissemination, 

In the latter part of their secondary hibernation, and before they 
scatter through the fields, their presence depends very much on two 
factors, namely, food and hibernating quarters. Once they begin 
moving they feed very little, and food seems to have no effect on the 
direction or amount of their movement. 

As this is, economically, the critical point in the Ufe of the adults — 
since where they collect, the eggs will be laid — they were watched 
carefuUy to see if there were any factors wliich governed their dis- 
persal tln-ough the fields. The amount of food and the size of the 

1 Subsequent rearing work in the laboratory proved that this was quite too early for oviposition. 



46 THE SUGAR-BEET WIREWORM. 

young growing beets were carefully taken into consideration, but the 
significance (.f tliese points, if there is any, is too sHght to be notice- 
able. Wliile the beetles have quite a strong flight, it was observed 
that they stay relatively near their hibernating places, so the most 
important factors at this period are the food and hibernating quarters 
which determined their presence earlier. These conclusions were 
arrived at from observations in fields aggregating several hundred 
acres. These factors, however, govern dissemination under normal 
conditions only. 

Other Factors Governing Dissemination. 

One fjictor wliich governs the direction of flight of the adults to 
some extent is the wind. This factor, however, has its hmitations, 
as the beetles can fly with ease against a very light breeze, and if 
the mud is blomng too strongly they do not fly at all. 

The floods which are apt to occur during the time the beetles are 
in secondary hibernation, or a little later, are probably of some 
importance — at least they must be so locally, where the San Gabriel 
River spreads over many acres of the beet fields almost every year. 
This river flows slowly and carries much rubbish, so that a large per- 
centage of the beetles carried along would probably survive. 

NATURAL CONTROL. 

Enemies and (^hecks to the Beetles. 

The adults of Limonius caUfornicus, being slow in their movements 
and conspicuous, are quite subject to the attacks of predaceous ene- 
mies. The good work of these enemies is further helped by the fact 
that the fields are quite bare at the time they are present in the 
largest numbers, while the beetles are concentrated for a part of the 
time. 

Unfortunately no figures can be given regarding the relations 
between the birds of the beet fields and the beetles, but a few observed 
facts may be given at this time. The only notes which bear on the 
insectivorous habits of the birds locally were taken on examination 
of the excrement of the California shrike (Lanius ludovicianus gam- 
heli) during the month of April. This excrement was made up almost 
entirely of coleopterous wing covers, and of these Limonius caUfor- 
nicus and Blapstinus sp. formed about 90 to 95 per cent. A very 
reasonable estimate would be that at least 70 to 80 per cent of the 
excrement examined was composed of fragments of Limonius caU- 
fornicus. 

Many observers have determined the fact that nearly all insectivo- 
rous birds eat different species of Elateridse readily, as the latter do 
not seem to be in the least distasteful to them. Following is a partial 



NATURAL CONTROL. 47 

list of the birds occuiTiiig in the beet fields, which huve been 
proven to be insectivorous.' Those marked (*) were especially 
abundant: 

Killdeer (Oxijechus vociferus). 

* Valley quail (Lophorti/x rali/omicus vallicola). 
Western nighthawlc ( Chordeiles virginianus henryi). 
Ash-throated flycatcher (Myiarchus cinerasceun rinerascens). 

* Western meadowlark {Sturnella neglecta) .'" 

* Brewer's blackbird (Euphagvs a/anocephalus) . 

* Native sparrow. 

* California shrike (Lanius ludovicianus gamheli). 

Next to the birds as insect destroyers can be ranked the predaceous 
beetles belonging to the family Carabidse, or ground beetles. Only 
two were noted, Cdlosoma cancellatum Esch. and C. semilseveLiec., but 
these proved to be important factors in the control of the beetles. 
Both of these occurred commonly throughout southern California. 
Sometimes as many as 15 to 20 would be noted in a single collecting 
trip. Calosoma cancelkitum occurred in the greater numbers. 

These predatory enemies are able to dispose of a large number of 
adults daily, as many outdoor observations proved. In one instance 
the examination of a large beet gave 31 live elaterids, 1 C. cancel- 
latum, and the remains of 117 elaterids. This beet had been exam- 
ined just two days previously, so this represented not more than two 
days' work. The rapidity of the work may be judged from the fact 
that the remains of a dozen of the elaterids were still moving their 
legs feebly when discovered. 

The carabids in feeding never touch the head or thorax, but bite 
off all or a part of the abdomen. As the abdomen, except when filled 
with eggs, contains little food it is readily understood how these 
ground beetles are able to destroy so many elaterids a day. The 
carabids did most of their feeding wliile the elaterids were in their 
secondary liibernation or early feeding period. They were especially 
valuable at this time, as they could dig under the beets and destroy 
the beetles collected there. 

These predaceous enemies — carabid beetles and birds — make a very 
good combination, as the beetles are an effective check early in the 
season, and later, when the elaterids are moving through the fields, 
the birds are at their best. 

Sudden and very severe storms probably act as further checks, but 
in a mild yeai", such as 1912, very few beetles were found to have been 
killed in the field. The adults are also attacked by a fungous dis- 
ease. This disease works well under laboratory conditions, but less 



1 See Senate Document No. 305, 62d Congress, 2d Session, p. 14, 1912. 

2 Mr. Bryant, in the Pomona Journal of Entomology, vol. 4, No. 3, speaking of the western meadow- 
lark, says, "Ground beetles are taken each month of the year." He then names Limonlus californkm 
among those taken. 



48 THE SUGAR-BEET WIREWORM. 

than 0.1 per cent were affected by it in the field. These two checks 
are of very httle importance. 

Enemies and Checks to the Larv^. 

Two characteristics of the wireworms, their tliick skins and their 
underf!:round life, cause them to be almost free from enemies. Of the 
10,000 larvae collected not one was noticed which was attacked by an 
internal parasite, although such parasites have been reported attack- 
ing Elateridse. Curtis ^ reports an ichneumon parasite on wdreworms 
in Great Britain, and says that Bierkander (of Sweden) also found 
them. Dr. S. A. Forbes ^ reports a single instance where a parasitic 
fly was reared from a wireworm. Very probably there are no efficient 
parasites in this group. 

The sugar-beet wireworm is, however, eaten readily by several 
kinds of birds whenever exposed. During the spring, when several 
of the fields at Dominguez, Cal. (6 miles from the ocean), were being 
plowed, it was noted that sea gulls (Larus sp.) were very abundant 
in the fields and followed the plow much as chickens do. They 
occurred by the hundreds and, as they are known to be omnivorous, 
they must have eaten numbers of wireworms. At this time and 
earher crows were also very abundant in the beet fields. During 
this period the wireworms were feeding at the surface on the left- 
over beets, and it was easy for the crows to reach them. As crows 
are famed as wireworm destroyers it is only reasonable to suppose 
that they killed large numbers of the larvae. This point will be 
investigated thoroughly in the future work on this insect. 

Larvae of a large carabid, probably Calosoma cancellatum Esch., 
have been found in the ground together with injured wireworms. 

In addition to bird and insect enemies one fungous and two bacte- 
rial diseases have been noted on this \\areworm. The fungus is only 
observed occasionally in the field, hence it is probably of little impor- 
tance economically. The bacterial disease of the mature larva was 
especially disappointmg, as it seemed to work only in certain cages. 
This naturally led to the belief that its presence was probably more 
the result of unfavorable conditions than the cause of them. The 
bacterial disease of the young larva did not promise much, as it did 
not seem to attack mature larvae under any conditions. 

As has been mentioned under the heading "Rearing cages used" 
(p. 21), many of the young wireworms which were kept in petri dishes 
died of a bacterial disease. This disease spread very rapidly, and 
there seemed no way to check it. Wherever it appeared, all the 
healthy wireworms were removed to a sterile cage and the infected 
cage steriUzed. The cages were examined several times a day and ail 

1 Farm Insects. By John Cnr(is, 1860, pp. ISl. 2 18th Rept. State Ent. 111., pp. 47, 1891-92. 



NATURAL CONTROL. 49 

wireworms were removed just as soon as they showed traces of the 
disease. In spite of all these precautions the disease spread un- 
checked until, within 10 days of its appearance, it had killed every 
wireworm in the petri dishes, to the number of about 1,000. 

The disease spread in the same way every time, and the wireworms 
killed by it were so characteristically colored that they could never 
be mistaken. When a larva became diseased, there was a very faint 
reddish coloration in the anterior portion of its body. When placed 
under the microscope, it looked as if the head and thoracic segment 
contained Uttle, brilliant red , oil globules. The following day the spec- 
imen would be a deep blood-red all over its body and so putrid that 
when picked up on a pin point it would fall to pieces. The larvae 
immediately surrounding it would show the faint red coloration and 
the following day they would be red and putrid, while the larvae 
nearest them would be showing signs of infection. When the dishes 
were not sterilized, all the larvae in a dish would be Idlled in from 
three to four days. 

That the red bacterium was the cause of the trouble was very 
strongly suggested by the fact that whenever one infected wireworm 
was placed in a sterile cage the disease immediately made its appear- 
ance. This was further borne out by the fact that where a whole 
infected wireworm was used to make a culture on agar, a pure culture 
of the red bacterium almost invariably resulted. When the cultures 
were made on agar, the colonies showed in their true color — a beau- 
tiful rich blood-red. (See PL VIII, fig. 1, p. 20.) 

It is interesting to note at this time that the mature wireworms 
which were exposed to infection by this bacterium were never affected 
by it. 

Everything considered, the larvae of Limonius californicus seem to 
be affected very little by their animal enenues and by their fungous 
and bacterial diseases, even when these latter are working under 
favorable conditions. 

Fungi Affecting the Pup.e and Eggs. 

A few pupae in the laboratory were attacked by a fungus and pre- 
sumably killed by it, as they died a short time afterward. As this 
occurred only in two cages and as no fungus-kiUed pupae were found 
out of doors, it is probable that this infection only occurs under arti- 
ficial conditions. Even if it did occur in the fields it would spread 
slowly, for during the time the insect is in the pupal stage the humidity 
is low and the soil in the fields is rather dry. 

A fungus which attacked and killed some of the eggs of Limonius 
californicus in the rearing cages in the laboratory would probably 
seldom or never occur out of doors. Even if it did it would not be 
6140°— Bull. 123—14 4 



50 THE SUGAR-BEET WIREWORM. 

of great economic importance, for when sound eggs were isolated in 
the cage in w^hich the fungus was working they were seldom attacked, 
showing that the fungus must spread slowly. Its appearance was 
probably the result of unfavorable artificial conditions. 

REMEDIAL MEASURES. 

Historical. 

Most of the literature thus far devoted to the study of wireworms 
from an economic standpoint has been a consideration of remedies. 
Probably no other insects have had more remedies tried for their 
control and with less success. Some of the remedies have been par- 
tially successful, but generally their cost has been such that their use 
for average crops is entirely impractical. One which would come 
under this head was a method tried on a small scale in Europe some 
time ago and consists in baitmg the wireworms and collecting them. 

Eleanor A. Ormerod,^ studying several species, gave as remedies (1) 
compacting the ground, (2) clearing off vegetation, and (3) making 
applications of gas lime. She stated that crop rotation was of little 
value. John Curtis ^ suggested as remedies frequent plowing to turn 
up the larvae, and appUcations of soot and lime. Mary Treat, ^ writ- 
ing on these insects, suggested spring and fall plowing and the trap- 
ping of larvae. Fall plowing as a remedy was recommended by C. M. 
Weed." 

The two most important sets of recommendations based on actual 
exhaustive experiments and careful study were those of Comstock and* 
Shngerland ^ at Cornell and S. A. Forbes "^ in Illinois. Their recom- 
mendations are quite different, Forbes suggesting a careful rotation 
of crops, while Comstock and Slingerland advise fall plowing for the 
destruction of the pupse and trapping the adults with poisoned bait. 

Tests of Suggested Remedies Against the Sugar-Beet Wire- 
worm. 

In testing remedies for the sugar-beet wireworm only those were 
tried which heretofore had promised at least partial success and which 
were at the same time thoroughly practical. 

attempts to destroy the adults with poisoned baits. 

Experiments with poisoned bait were carried on against the adults, 
using the bait much after the method suggested by Comstock and 

1 Manual of Injurious Insects and Methods of Prevention. By E. A. Ormerod, 1890, pp. 109. 

2 Farm Insects. By John Curtis, 1860. 

3 Injurious Insects of Farm and Garden. By Mary Treat, 1882. 
* Insects and Insecticides. By C. M. Weed, 1891. 

» Bull. 33, Cornell Agr. Exp. Sta., 1891. 
« 18th Rept. State Ent. 111., 1891. 



REMEDIAL MEASURES. 51 

Slingerland.^ These experiments from the first gave entirely nega- 
tive results, as the beetles could not be induced to feed on any kind 
of foliage, either in the poison or check cages. Further experiments 
were carried on, using such substances as bran, shorts, alfalfa meal, 
and ground beet roots. The last bait was the only one which gave 
any promise, and this proved successful only under laboratory 
conditions. Where the poisoned bait was applied in the cages a 
few beetles were killed by it, but where it was tested in the field it 
gave negative results. This was probably on account of the light 
feeding habits of the adults and the abundance of food in the fields. 
The poisons used in the bait were Paris green, arsenite of zinc, arse- 
nate of lead, and strychnine. 

FALL PLOWING FOR DESTRUCTION OF THE PUPJE. 

The destruction of the pupa? by cultivation, while probably it 
has never been tested under field conditions, has been recommended 
by many students of this group because it is directed against the 
most helpless stage of the insect. From observations made of the 
results obtained by disturbing pupae in the laboratoiy cages, there 
can be no doubt that this remedy would prove beneficial, since not 
only would it break open many cells and kill the ])up?e mechanically, 
but it would also disturb the rest so that they would come out earlier 
in the spring and be subject to the attacks of their bird enemies. 
This fall plowing would have to be quite deep (9 to 10 inches), and 
very thorough, to be effective. 

The main objection to this remedy is that three or four years 
must elapse before the benefits derived from it become apparent. 
One point will serve to illustrate this. It was reported through 
Mr. R. S. Vaile, the horticultural commissioner of Ventura County, 
Cal., that in one instance, in a field which had been fall-plowed, the 
wireworms were worse than in any of the surrounding fields. This 
was doubtless true, and would have been possible had the plowing 
killed every pupa. The wireworms which do the main damage for 
at least the next two years are alreadj^ in the soil at the time of the 
plowing and are unaffected by it. This is true because the wire- 
worms are not of sufficient size to be very injurious until the third 
year. Mr. Vaile states that it is a rule with many of the bean grow- 
ers in his county to fall-plow their fields; and that any benefits which 
might have resulted from such a treatment have never been notice- 
able. He adds, however, that the thoroughness of this plowing 
might be improved upon in many cases. 

1 Bui. 33, Cornell Agr. Exp. Sta., 1891. 



52 



THE SUGAE-BEET WIREWORM. 



EXPERIMENTS WITH DETERRENTS AGAINST THE WIREWORMS. 

A fairly exhaustive series of experiments was carried on, using 
repellent substances against the larvae. While some of these experi- 
ments are a repetition of the work done by Comstock and Slinger- 
land, the greater number are rather an addition to their work. From 
the start this work promised little, but was undertaken because, if 
successful, it would afford a remedy which would give immediate 
results, and this is most important with this insect. 

A system was adopted regarding both the nature of the experi- 
ments and the times of application. Three tests were given each 
experiment in the spring, when the larvae were most active, and a 
test was given in the fall just before their hibernation period. The 
last one was on a small scale and was carried on merely for the sake 
of added evidence. 

Flowerpots were the cages used in the spring experiments. It 
was found that if the hole in the bottom was stoppered with cork, 
none would escape in the time of the experiment. It was also 
noted that where about half an inch of dry soil was placed on top 
of the damp soil of the cages the wireworms would never come 
entirely to the surface. This treatment, then, allowed the flower- 
pots to be buried to the surface of the soil out of doors, and with the 
exception that the larvae were a little crowded it gave outdoor 
conditions. 

In the first test of each experiment 50 larvae were used and the 
test covered 20 days. In the two remaining tests in the spring 25 
larvae were used each time and the ex})eriment was allowed to run 
for 30 days. In the experiments with deterrents the following sub- 
stances were tested: 



(1) Carbolic acid. 

(2) Carbolic emulsion. 

(3) Turpentine. 

(4) Kerosene. 

(5) Kerosene emulsion. 

(6) Whale-oil soap. 

(7) Potassium cyanid solution. 

(8) Potassium cyanid solid. 

(9) Copperas solution., 
(10) Copper sulphate. 

These deterrents were used on beet and lima-bean seeds, both of 
which are attacked by this species. It was hoped that in these ex- 
periments a deterrent could be discovered for protecting the tender 
roots until the plant had secured a fair start. If this could be ac- 
complished the injury due to wireworms would be materially lessened. 



(11) Potassium sulphid solution. 

(12) Tar water. 

(13) Ash water. 

(14) Nicotine sulphate. 

(15) Free nicotine solution. 

(16) Cresol (so-called coal-tar creosote). 

(17) Salt solution. 

(18) Lead chromate. 

(19) Dry sulphur. 



I 



REMEDIAL MEASURES. 



53 



CARBOLIC ACID. 

Some seeds were soaked iii a 10 per cent solution of carbolic acid 
overnight, were allowed to dry for some time, and were then planted 
in the pots. Fifteen were planted m the cage which contained the 
50 larvae. This cage was broken up ui 20 days and exammed, with 
the following results: Two seeds were destroyed before germination; 
seven after germmation, and six were untouched; tliree larvae were 
dead. In the check cage three seeds were untouched; most having 
been destroyed just after germination, and one larva was dead. 
The check cages gave even less favorable results, so it seems clear that 
the carbolic acid has little effect as a deterrent. 

CARBOLIC EMULSION. 

Carbolic emulsion was made by using the following ingredients in 
the proportions named : ^ 

Crude carbolic acid gallons . . 5 

^^^lale-oil soap pounds . . 40 

Water (hot) gallons. . 40 

The seeds treated were soaked m this emulsion overnight. After 
drying ^ in the sun for two hours they were planted. The results of 
the experiments are summarized in the following table: 

Table II. — Experiments with carbolic emulsion as a deterrent against the sugar-beet 

wireu'orm . 



Larvae 


Seeds 


Seeds attacked. 


Seeds un- 






used. 


used. 


Before 
germina- 
tion. 


After 

germiaa- 

tion. 


touched. 


50 


15 


2 


7 


6 


50 


15 


10 


3 


2 


25 


10 


1 


7 


2 


25 


10 


4 


6 





25 


10 


3 





2 


25 


10 


4 


2 


4 



Larvae 
missing. 



Larvae 
killed by 
fungus. 



Dura- 
tion of 
test. 



Experiment. 

Check 

Experiment, 

Check 

Experiment, 
Check 



Days. 



20 
20 
30 
30 
30 
30 



A glance at the foregoing summary shows that while carbolic acid 
might possibly be of value, it can not at this time be considered a 
practical remedy for wireworms. 



TURPENTINE. 



Seeds were soaked overnight in turpentine and after being allowed 
to dry were planted in the cages containing the wireworms. The 
turpentine had affected the seeds considerably and all of them were 
more or less '^ blistered," 



1 Essig, Pomona Journ. Ent., vol. 2, no. 3, p. 252, 1910. 

- The seeds were dried in these experiments because, if used under field conditions, they would have to 
be treated in this manner before they could be used in a beet planter. This would be the only practical 
way the emulsion could be applied. 



54 THE SUGAR-BEET WIREWORM. 

Table III.— Experiments with turpentine as a deterrent against the sugar-beet vnreworm. 





Larva; 
used. 


Seeds 
used. 


Seeds attacked. 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
killed by 
fungus. 






Before 
germina- 
tion. 


After 
germina- 
tion. 


Dura- 
tion of 

test. 


Experiment 


50 
50 
25 
25 
25 
25 


15 
15 
10 
10 
10 
10 


3 
3 
4 

8 

7 


5 
4 
3 
2 

3 


7 
8 
3 
3 
2 






1 
3 
4 





1 
2 

1 


Days. 
20 
20 
30 
30 
30 
30 


Check 


Experiment 

Check 

Experiment 

Check 



A glance at columns 6 and 7 of Table III shows that there is little 
difference between the treated and untreated seeds — too little to 
promise much for this method. 



KEROSENE. 



Kerosene was given a trial as a deterrent in spite of the fact that it 
gave negative results in the experiments of Comstock and Slmgerland, 
The seeds were treated by soaking m kerosene overnight. The kero- 
sene in some instances removed part or all of the skin from the seeds. 
The results are summarized below. 

Table IV. — Experiments with kerosene as a deterrent against the sugar-beet wireworm. 





Larvae 
used. 


Seeds 
used. 


Seeds attacked. 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
killed by 
fungus. 






Before 
germina- 
tion. 


After 
germina- 
tion. 


tion of 
test. 




50 
50 
25 
25 
25 
25 


15 
15 
10 
10 
10 
10 


8 
12 

8 
10 

7 
8 


3 
1 
1 

1 
2 


4 
2 
1 

2 



2 

1 
4 




2 

6 

1 




Day.<i. 
20 


Check 


20 




30 


Check 


30 


Experiment 


30 


Check 


30 







This table shows that while treated seeds are a little less liable to 
attack before germination yet in the long run there is little difference 
between treated and untreated seeds. Germination tests carried on 
at the same time show that kerosene kills some of the seeds, so this 
would at least offset any benefits which might possibly be derived by 
protection. 



KEROSENE EMULSION. 



As the pure kerosene showed a weak tendency to keep the wire- 
worms away temporarily it was thought that if some distasteful sub- 
stance were mixed with it the combination of the two might be more 
successful. To this end kerosene emulsion was prepared by using 
whale-oil soap. The seeds were soaked in this overnight and then 



REMEDIAL MEASURES. 



55 



dried in the sun. The seeds did not chy thoroughly and tended to 
adhere to one another. This would be a great disadvantage, as it 
would be hard tp run these treated seeds through a planter. The 
following summary further shows its impracticability: 

Table V. — Experiments with kerosene emulsion as a deterrent against the sugar-beet 

unreworvi. 





Larvae 
used. 


Seeds 
used. 


Seeds attacked. 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
killed by 
fungus. 


Dura- 
tion of 

test. 




Before 
germina- 
tion. 


After 
germina- 
tion. 




50 
50 
25 
25 
25 
25 


1.5 
10 

10 
10 
10 


6 
10 

4 
6 
4 


2 
3 
3 
6 
3 
2 


2 
7 


1 
4 



1 

2 
2 
5 


2 
1 






Days. 

20 


Check 


20 


Experiment 


30 


Check 


30 


Experiment 

Check 


30 
30 







WHALE-OIL SOAP. 

The seeds used in the whale-oil-soap experiment were treated in 
two different ways. At first they were coated with the soap, but 
this method proved impractical (1) because the seeds could not be 
used m a planter and (2) because they tended to rot. The seeds 
were then treated by soaking in a concentrated water solution of the 
whale-oil soap. This second method overcame the objections to the 
jSrst method. The results are summarized below. 

Table VI. — Experiments with ichale-oil soap as a deterrent against the sugar-beet 

wireirorm. 





Larvae 
used. 


Seeds 
used. 


Seeds attacked. 




Larvae 
missing. 


Larvae 
killed by 
fungus. 


Dura- 
tion of 

test. 




Before 
germina- 
tion. 


After 
germina- 
tion. 


Seeds un- 
touched. 


Experiment.. 


50 
50 
25 
25 
25 
25 


15 
15 
10 
10 
10 
10 


10 
12 
4 
10 
f> 
8 


2 
1 
3 

4 
2 


3 
2 
3 










f. 


Days. 

20 


Check 


20 


Experiment.. 


1 3 
4 i 1 


30 


Check 


30 


Experiment 

Check 


1 







30 
30 







This table shows that the treatment of the seeds with whale-oil 
soap holds little promise of success. 



tar water. 



Smce satisfactory" results in seed protection by coating the seeds 
with tar have been reported, it was thought possible that similar 
results might be obtained by soaking the seeds in tar water. In 
this way it should give the benefits of coating the seeds with tar, 



56 



THE SUGAE-BEET WIREWORM. 



and at the same time not have the disadvantage of causing the seeds 
to rot. This water is procured by allowing a mass of coal tar or 
pine tar to stand in water for some time. The water becomes 
slightly colored and smells very strongly of tar. A very little tar 
will suffice for treating a large amount of water. 

The seeds were treated by allowing them to soak in this water 
overnight, and they were then planted. They smelled quite strongly 
of tar even after they were allowed to dry partially. The results 
obtained are shown in the following summary: 

Table YII. — Experiments with tar water as a deterrent against the sugar-beet vireuorm. 





LarvjB 
used. 


Seeds 
used. 


Seeds attacked. 


Seeds un- 
touched. 


Larvee 
missing. 


Larvae 
killed by 
fungus. 






Before 
germina- 
tion. 


After 
germina- 
tion. 


tion of 

test. 


Experiment 

Check 

Experiment 

Check 

Experiment 

Check 


.-.0 
.50 
25 
2.5 
25 
25 


15 
15 
10 
10 
10 
10 


3 
4 
.5 
6 

7 


2 
4 
3 
2 
2 
3 



8 
3 
3 
2 





1 
1 

4 


1 

2 
1 
2 
1 


Ixiyx. 

20 
20 
30 
30 
30 
30 



In spite of the fact that the table seems to indicate that tar water 
is ineffectual, this method is to be given a more extensive trial next 
spring. 

ASH WATER. 

Ashes have long been used and recommended as a deterrent 
against various msects, and especially wireworms. It has been 
mentioned previously that the beetles appear to be driven out by 
ashes. About the only way that ashes could be used on a large 
scale would be to soak the seeds in water which had been used to 
leach out ashes. This method was used, the seeds being partially 
dried before planting. The following summary shows that any 
benefits which might have been derived from the use of this method 
are too small to be of much importance. 

Table VIII. — Experiments irith ash water ns a deterrent against the sugar-beet vireworm. 





Larvae 
used. 




Seeds attacked. 


Seeds un- 
touched. 






Dura- 
tion of 
test. 




Seeds 
used. 


Before 
germina- 
tion. 


After 
germina- 
tion. 


i 


Experiment 


50 
50 
25 
25 
23 
25 


15 
15 
10 
10 
10 
10 


10 
6 
4 

4 


2 
2 
H 
1 
2 


3 
2 

2 

4 


' 2 

1 
7 

2 


Days. 
20 


Check. 


20 


Experiment 


30 


Check 


30 


Experiment. . 


2 

5 


1 



30 


Check 


30 



BEMEDIAL MEASURES. 



51 



NICOTINE SULPHATE. 



Some seeds were soaked overnight in nicotine sulphate and dried 
before planting. This sulphate, which is advertised to contain 40 
per cent nicotine, is a dark, \nscous liquid and smells very strongly 
of nicotine. When used pure it tended to rot many of the seeds- 
The best germination results were obtained when it was diluted 
about one-half 's\'ith water. The summary shows that it could not 
be recommended as a deterrent. 



Table IX. 



-Experiments with nicotine sulphate as a deterrent against the sugar-beet 
tnreworm . 





Larvae 
used. 


Seeds 
used. 


Seeds attacked— 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
killed by 
fungus. 


Dura- 
tion of 
test. 




Before 
germina- 
tion. 


After 
germina- 
tion. 


Experiment 

Check. 


.50 
50 
2.5 
25 

25 
25 


15 
15 
10 
10 
10 
10 


8 
10 

6 
10 

8 


7 
3 
2 


2 



2 
2 
5 


1 




1 

4 




2 
1 
1 
1 
fi 



Days. 
20 
20 


Experiment. 


30 


Check. 


30 


Experiment 

Check 


30 
30 







FREE NICOTINE. 



Seeds were soaked in nicotine solution overnight. This fluid, 
which contains free nicotine in water, has a very sharp nicotine odor 
and is also 40 per cent nicotine. As the results obtained in two out 
of the three tests were negative, its value as a deterrent must be 
slight. Some of the bean seeds were riddled by the wireworms. 
The results are shown below: 

Table X. — Experiments vnthfree nicotine as a deterrent against the sugar-beet wireworm. 





Larvae 
used. 


Seeds 
used. 


Seeds attacked— 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
killed by 
fungus. 


Dura- 
tion of 

test. 




Before 
germina- 
tion. 


After 
germina- 
tion. 


Experiment 

Check 


.50 
50 
25 
25 
25 
25 


15 
15 
10 
10 
10 
10 


4 
3 
3 

4 


7 
4 
3 
2 
2 
2 


4 
8 
4 
3 
1 
4 




3 

1 

5 


3 


1 
2 



Days. 
20 
20 


Experiment 

Check. 


30 
30 


Experiment 

Check 


30 
30 







Cresol, so-called coal-tar creosote, was tried in these experiments 
because it is used quite successfully in keeping dermestid larvae out 
of collections. It is a thin liquid, rather dark in color, and with a 
strong tarry odor. The seeds were soaked in it overnight. The 



58 



THE SUGAR-BEET WIREWORM. 



results, which are summarized in the following table, do not promise 
much for the use of this substance in protecting seeds. 

Table XI. — Experiments with cresol as a deterrent against the sugar-heet wireworm.. 





Larvae 
used. 


Seeds 
•used. 


Seeds attacked— 


Seeds un- 
touched. 


Larvae 
missing. 


Larvae 
kDled by 
fungus. 


Dura- 
tion of 
test. 




Before After 
germina- germina- 
tion, tion. 


Experiment 

Check 

Experiment . 


50 
50 
25 
25 
25 
25 


15 
15 
10 
10 
10 
10 


8 
10 
6 
4 
5 
7 


3 
2 
2 
6 
4 
3 


4 
3 
2 

1 



1 

2 

4 


1 



2 
1 


Days. 
20 
20 
30 


Cheek 

Experiment 

Check 


30 
30 
30 



OTHER SUBSTANCES TESTED AS DETERRENTS. 

The other deterrents will be considered very briefly, since, with 
the possible exception of two, none gave much promise of ultimate 
success. 

Copperas solution. — Seeds soaked overnight in a copperas solution, 
dried, and planted in the pots were almost as readily eaten as those 
in the check cages. 

Copper sulphate. — Copper sulphate did not give much promise as a 
deterrent, as the seeds soaked in a solution of it overnight were eaten 
readily by the wireworms, and with apparently no iU effects. 

Potassium sulphid. — -Seeds treated with a concentrated solution of 
potassium sulpliid appeared neither distasteful nor injurious to the 
wireworms. 

Salt.— The seeds treated by soaking in a salt solution seemed for a 
time to be partially immune to the attack of wheworms. By the 
time several tests were completed, however, it was seen that while 
they were more immune from attack just before germination, enough 
were killed just after germmation to make tMs procedure useless 
from a practical standpoint. 

Sulphur. — Some seeds were coated with a paste made of equal parts 
of sulphur and flour, and after being allowed to dry were planted. 
When examined later many had rotted and the rest had been riddled 
by the wireworms. Some of the larvae were partially covered with 
sulphur, but did not seem in the least inconvenienced. It was con- 
sidered that this experiment would give negative results, since the 
sulphur, kept under the damp cool soil, would not give off fumes to 
any extent, and hence its best effect would be lost. 

Lead chromate. — Seeds treated as m the foregomg experiment, but 
using lead chromate in place of sulphur, were not protected in the 
least, nearly every seed being drilled tlirough m several places. 



KEMEDIAL MEASURES. 59 

THE USE OF POTASSIUM CYANID AGAINST THE WIREWORMS. 

Potassium cyanid was one of the first remedies tested for the wire- 
worms, because it has the properties both of an excellent deterrent 
and a deadly poison. Used as a deterrent, the seeds were treated in 
two different ways. In the first the cyanid was used as a solid and 
drilled in with the seed. This method affords excellent protection 
to the seed, but the drawbacks connected ^\ith it have thus far made 
it impracticable. The cyanid burns the seed wherever it comes in 
contact with it, and when germination beguis, it burns the tender 
roots. Another argument against its use for this crop is its cost. In 
the second method of seed protection the seeds were soaked over- 
night in a solution of cyanid in water, dried, and planted. In this 
method it was also quite effective as a deterrent, but unfortunately 
its effects on the roots were such that it could not be used. At the 
present time it seems very doubtful if the cyanid can be used in such 
a strength that it will keep away the wireworms and at the same 
time not harm the plants. Tliis point is gomg to be tested further. 

T\^iile these experiments were being carried on it was noted that 
in some of the cages most or aU of the wdre worms had been killed. 
These larvae had the appearance of having been kiUed by a fungus, 
but as their bodies were not filled with the fungus it was apparent 
that they had been killed in some other way. It was thought that 
perhaps they had been killed by the fumes of the cyanid, and later 
experiments seemed to bear out this point. With this in view, many 
expermients were carried on in an attempt to discover some good 
method for the application of the cyanid. From these, two plans 
were selected for final trials, one in which the cyanid was used as a 
solid, and the other in which it was used as a liquid. The results are 
given below. 

According to the fu'st plan the cyanid was drilled into the ground 
much after the method used for fertiUzers. This plan was finally 
given up, as the cyanid was not distributed evenly through the soil, 
and therefore had to be appUed more heavily than was necessary in 
order to be effective. As the cyanid is very destructive to plant 
growth it is readily seen that it would have to be used as sparingly 
as possible. 

The method of using the liquid consisted in making a solution of 
the cyanid in water and applying it evenly over the land. This 
could then be made to permeate the soil to any depth by migation. 
By this method the cyanid is used sparingly, as it is evenly applied. 
Unfortunately it has been impossible to try this remedy thoroughly, 
up to the present time. In all the experiments where this method 
was employed its killing power was very good. To test it further, 
it was applied in a cage containing beets, with the result that both 



60 THE SUGAK-BEET WIEEWORM. 

beets and wireworms were killed. It was used several times more, 
and in weakened solutions, but invariably the results were the same. 
By this time the season was so far advanced that experiments along 
this hne had to be given up for the year. The conclusions that seem 
justified from this experiment at the present time appear to be that 
the wareworms may be killed by applications of a solution of potassium 
cyanid to the soil, but that the beets are also killed by the same treat- 
ment. It is a question whether a certain strength of cyanid can be 
found which wall kill the wireworms and spare the beets. Possibly, 
however, the wdreworms can stand a stronger application of the 
cyanid than the beets can. As this is the only insecticide which has 
given promise of good results against the wdreworms, it wall receive 
further careful tests. The possible effect of this cyanid on the soil 
and future crops is also an interesting question, and one which wnU 
have to be investigated. There is a possibility that this cyanid 
might be applied directly after the crop is removed and before the 
wireworms have become dormant for the winter. 

EXPERIMENTS WITH POISONED BAIT AGAINST THE WIREWORMS. 

In the experiments in the use of poisoned bait against the wire- 
worms the points which were chosen for solution were, (1) to find a 
substance for the bait wliich would be very attractive to the wire- 
worms, and (2) to find a poison to go with it which would certainly 
kill the larvffi. Thus far success has not been attained in the solution 
of either. The following materials have been experimented with as 
bait: 

Beans. Bran. 

Com. Alfalfa meal, 

rommeal. Shredded beets. 

Of these the only ones which have proved attractive enough to be 
used with the poisons were beans, corn, and shredded beets. Series 
of experiments were conducted using each bait with every poison, 
and checks were employed in each. The following poisons were used: 

(1) Lead cliromate. (4) Paris green. 

(2) Potassium cyanid. • (5) I^ead arsenate. 

(3) Strychnine. (6) Zinc arsenite. 

The first four named, being insoluble, were applied to the bait in 
paste form with flour. In the case of every poison except the cyanid 
the wireworms were observed eating the bait, and if they suffered 
any ill effects from it they failed to show it to a noticeable degree. 
The bait containing the cyanid was eaten sparingly on account of 
its deterrent qualities. Wireworms were found dead in some of the 
cages in wliicli potassium cyanid was used, but whether theii* death 



Bui. 123, Bureau of Entomology, U. S. Dept. of Agricultur 



Plate XIX. 




Fig. 1.— Field of Young Beets at Age when they Begin to be Partially Safe 
FROM Severest Injury by the Sugar-Beet Wireworm. (Original.) 





jiii^ 






^^^^^^^ 


^9I^^^PIS1P 


i:^m-Mm^>A 


j*»".w^ia ■ iMiTTii wmi niww m\ 



Fig. 2.— Beet Field, Showing Conditions Favorable for Increase of Wire- 
worms. Weed Hedges which Shelter Adults in Secondary Hibernation. 

(Original.) 



Bui. 1 23, Bureau of Entomology, U. S. Dept. of Agricultur 



Plate XX. 




j|. 123, Bureau of En1o:nology, U. S. Dept. of AgriCL 



Plate XXI, 




123, Bureau of Entomology, U. S. Dept. of Agiiculture. 



Plate XXII. 




m^M:^^' ^i'Vti^ttV ?%&■ ,w >> '" f F^-^Jt 









UJ O 

X - 



I- (- 

"CO 



O u. 
O ^ 



O CO 
^ < 






CO •- 

<^ ^ 

< o 

C02 

UJ UJ 



o 



3ul 123, Bureau of F.ntotr,ology, U. S. Dept. of Agriculture. 



Plate XXIIl. 




Fig. 1.— Beet Fields Separated By Strip of Alfalfa. (Original.) 



it.iiiifi.' i'-ll t id 4 i5«^ "^/* '».'*'' > 1 1' *' 




Fig. 2.— Field of Alfalfa Adjoining Field of Sugar Beets. (Original.) 
CONDITIONS FAVORING THE SUGAR-BEET WIREWORM. 



REMEDIAL MEASURES. 61 

was due to eating the })oison or to tlie effect of fumes has not been 
determined. 

The results in the use of strychnine and potassium cyanid have 
been quite well verified in an entirely independent series of experi- 
ments carried on by Mr. R. S. Vaile. 

From the foregoing it can be seen that the experiments thus far 
tried in the use of poisoned bait against the sugar-beet wireworm 
have been far from satisfactory. They are to be continued in future 
work. 

EXPERIMENTS WITH GUANO FERTILIZER. 

The only fertilizer tested on tlie wireworms was a mixture of bird 
and bat guano, a South American product, which is chiefly nitroge- 
nous and is characterized by a strong and lasting odor of ammonia. 
It was lioped that the strong ammonia odor would drive the wire- 
worms deeper into the soil. The results from its use thus far — it 
has been tried only on a small scale in the laboratory — seem to indi- 
cate that it would have to be used at the rate of from 8 to 10 tons 
per acre to be partially effective. As this is many times heavier 
than an average dressing for the soil it would probably be impractical 
to use it. 

PROTECTION OF BEETS BY EARLY PLANTING. 

The protection of beets by early planting is a remedy which was 
early suggested by Mr. H. M. Russell and has since been given a 
practical test on a large scale. The advantage of tliis method is 
very plain. When the beets are planted early the plants are quite 
hardy and the roots are swollen by the time the wireworms are doing 
their worst injury. (See PI. XIX, fig. 1.) These swollen roots can 
stand a severe attack without having their sap supply cut off, and in 
consequence a much smaller number of them are killed. 

Mr. H. J. Mayo, one who grows sugar beets on a large scale in both 
Los Angeles and Orange Counties, wi'ites as follows concerning early 
planting : 

* * * In the season of 1911 I planted early and the results were very good, 
especially on the heavy land, as the beets seemed to get a start, and the worms did not 
seem to affect them so much, although they were in the ground and from examinations 
that I made they worked on the beets; but where the beets got the start the worms 
did not bother them so much. 

In my opinion early planting vvill relieve a great deal of the danger of the wireworm. 

Clean Culture against the Adults. 

The following in regard to remedial measures is the result neither 
of theory nor of experiment. It was suggested to the writer by 
observations taken in the field at the time the liibernating beetles 



62 THE SUGAR-BEET WIREWORM. 

were being collected. It was suggested also by the different states 
of affairs noted in different fields wliere various systems of culture 
had been practiced. These observations were carefully made in 
fields aggregating over 600 acres, and daily during a period covering 
about two months. 

Two different methods are practiced by the growere in disposing 
of the beet tops wliich remain in the field (see PI. XX) after the crop 
has been harvested. Some growers leave them in the field to be 
plowed under and act as a fertilizer, while others use them for stock 
feed. In the latter method, which may be spoken of as clean culture, 
the beet tops are either disposed of by pasture (PL XXI) or they are 
hauled from the field (PI. XXII). The tops are removed best by 
pasturing either with cattle or sheep. 

The tops which are left for. fertihzer are supposed to be plowed 
under, l)ut by the time the land has been harrowed several times, and 
planted, not a few have reappeared on the surface. Then as the 
beetles appear in the spring and enter their secondary hibernation 
they find excellent shelter and feeding places (see PL XIX, fig. 2), and 
most of them remain in the field near the place where they emerged 
and are able to pass this critical period of their lives safely. On the 
other hand, where the tops and old beets have been cleared off, the 
beetles find no place to hide, and consequently move to other fields 
in search of shelter. Very few can hide under clods or in the soil on 
account of intermittent rains. 

One illustration of the effects resulting when beets are left in the 
fields will be sufficient, for this same state of affairs was found to 
exist in all the fields examined. 

The beet fields A, B, and C adjoined one another as shown in the 
diagram (fig. 9). At the right of C was a fiehl of alfalfa. In A the 
beet tops had l)een left in the field to act as a fertilizer; in B and G 
they had been cleared off. During the preceding year the field G 
had suffered from mreworm injury as much, if not more, than any 
field in the Compton district. On this account there must have been 
many mature wireworms there, and consequently many beetles 
emerging, yet when the beetles were collected in these fields hardly 
any were found in B and C, and they were taken in A literally by 
thousands. As an experiment, about oO old beets were scattered in 
the field G, along the line c c. These beets were inspected daily from 
this time on, and found to shelter large numbers of adults, even though 
none had been taken previously in G. Conditions in the other two 
fields remained as before, no beetles, or very few, being found in B 
while A yielded its usual number. 

A simple conclusion can be drawn from these observations. The 
beetles collected only where they could find shelter, and those which 
emerged from perfectly clean fields had either to move to other fields 



REMEDIAL MEASURES. 



63 



B 



where they could find shelter or to remain where they were, exposed 
to the attacks of their predaceous enemies, the birds. In the instance 
cited probably many were eaten by birds, as these were quite abund- 
ant at the time, and the fields were bare. 

In the observations dealing with the dispersal of the beetles 
througliout the fields it was determined that for the greater part the 
beetles remain and lay eggs near the place where they have been 
feeding. From this it is easy to see that in the fields which contain 
the greatest number of old beets and beet tops the largest number of 
beetles wiH deposit their eggs. As the wireworms can not travel 
very far from where the eggs are laid it is readily seen that large 
numbers of beetles in a field are the forerunners of large numbers 
of wireworms in that field later, with their resulting injuries to the 
crop. 

A condition leading to the successful hibernation and dispersal of 
wireworms is illustrated in Plate XXIII, figures 1 and 2. In these 
instances the immediate proximity of alfalfa fields to those containing 
beets affords effective shelter for 
the liibernating beetles, and, as 
alfalfa is only second as a host to 
beets, provides abundant food for 
a continual supply of larvae and 
adults. Reinfestation under such 
conditions is naturally very hkely 
to occur through the migration of 
the beetles from the alfalfa to the 
beets, and both crops may thus 
be injured. 

The main drawback to clean cul- 
ture is that even where it is prac- 
ticed faithfully several years must pass before positive results will 
be apparent. As has been stated, the same thing is true with regard 
to fall plowing for the destruction of the pupge. This would be 
advantageous in one way, however, in that the benefits would be felt 
for two years after the treatment had been discontinued. The main, 
difficulty is that a grower, after practicing this remedy for two years, 
might suffer heavily from wireworm injury, become discouraged, 
and stop the treatment. The only way to give this remedy a fair 
trial would be to practice it faithfully and wait until the third or, 
better, the fourth year before drawing conclusions. 

The greatest advantage of this remedy is that it is entirely feasible 
and, being cultural in character, is also entirely practical, regardless 
of the crop grown. For the best results it should be practiced in 
conjunction with faU plowing, and to reduce the injury from the 
wireworms already in the soil early planting should be employed. 



C 



ALFALFA 
F/ELD 



Fig. 9.— Diagram of beet fields, to illustrate the 
effect of clean culture in reducing injury by the 
sugar-beet wireworm. (Original.) 



64 THE SUGAR-BEET WIREWORM. 

Considering that all the growers have idle horses during the late fall, 
the plowing would not appear to be a large item of expense, espe- 
cially when its value to the soil is taken into consideration. 

In conclusion it may be saf el}^ stated that the clean-culture remedy, 
especially when reenforced by fall plowing and early planting, is easily 
the most promising remedy which has thus far come under observa- 
tion during the sugar-beet wireworm investigations. 

SUMMARY. 

(1) The sugar-beet wireworm kills the beet plant by injuring the 
root. It is most injurious while the beets are young and is destructive 
only in the wireworm or larval stage. 

(2) The life cycle probably covers four years. About one month 
each is required for the egg and pupal stages; seven to nine months 
for the adult stage, during the greater part of which the beetle is in 
hibernation; and about three years, or the rest of the time, for the 
larval stage. 

(3) Thus far it seems to be impractical to employ remedies against 
the larvae. As these live underground and are protected by a thick 
integument it is difficult to injure them. They also seem able to eat 
a certain quantity of many poisons and deterrent substances with 
safety. 

(4) Plowing in the fall is a fair remedy against the pupae, but at 
that time of the year the soil is dry in southern California and is 
turned up in large clods; consequently many pupae escape destruction. 

(5) Much of the injury to the beets may be avoided by early 
planting, thus giving the roots a good start before the wireworms 
are doing their most extensive feeding. 

(6) Clean culture against the adults, by compelling them to seek 
shelter elsewhere and exposing them to the attacks of their bird 
enemies, seems to be the most practical remedy found thus far for 
this insect. The efficiency of this remedy would be increased if fall 
plowing and early planting were used witli it. 

BIBLIOGRAPHY. 

1843. Mannerheim, G. G. von.— Bull. Soc. Imp. Nat. Mos^cou, vol. 16, p. 283, 1843. 

Original description of Limonius californicus under the name 
Cardiophorus californicus. 

1912. Vaile, R. S.— Ann. Rept. Hort. Comm. Ventura County, 1912. 

Brief account of damages, and remedies proposed for experiment. 



INDEX . 

Page. 
Alfalfa, food plant of Limonius californicus 1 1, 16, 17, 35 

meal, poisoned, as bait for sugar-beet wireworm 60 

Amaranthus retroflexus, food plant of Limonius californicus 16 

Arsenate of lead in poisoned baits against sugar-beet wireworm 60 

beetles 51 

Arsenite of zinc in poisoned baits against sugar-beet wireworm 60 

beetles 51 

Ash water against sugar-beet wireworm 52. 56 

Aster, wild, food plant of Limonius californicus 16 

Bacterial diseases of Limonius californicus larvae 48-49 

Beans, food plants of Limonius californicus 12, 16, 17 

poisoned, as bait for sugar-beet wireworm 60 

Beet roots, food of Limonius californicus beetles 35-36 

sugar, food plant of Limonius californicus 11. 12, 16, 17 

Beets, injury by wireworms, Limonius californicus 26-27 

shredded, poisoned, as bait for sugar-beet wireworm 60 

Blackbird, Brewer's. (See Euphagus cyanocephalus.) 

"Blacksmiths," colloquial name for Elaterida? 13 

Blapstinus sp. in sugar-beet fields with Limonius californicus 13 

prey of Lanius ludovicianus gambeli 46 

Bran, poisoned , as bait for sugar-beet wireworm 60 

Brassica niger, food plant of Limonius californicus 16 

Cages for rearing Limonius californicus 21-22, 36-37 

Calosoma cancellatum, enemy of Limonius californicus 47, 48 

semilaeve, enemy of Limonius californicus beetles 47 

Carabidse, enemies of Limonius californicus beetles 47 

Carbolic acid and carbolic emulsion against sugar-beet wireworm 52, 53 

Cardiophorus seneus, in sugar-beet fields, comparison with Limonius californicus. 13 

californicus =Limonius californicus 13 

original description 14 

crinitus (?), in sugar-beet fields, comparison with Limonius cali- 
fornicus 13 

Chordeiles virginianus henryi, enemy of Limonius californicus beetles 47 

Chrysanthemum, food plant of Limonius calif oi-nicus 16 

Coniontis sp. in sugar-beet fields with Limonius californicus 13 

Copperas solution against sugar-beet wireworm 52, 58 

Copper sulphate against sugar-beet wireworm 52, 58 

Corn, food plant of Limonius californicus 11, 12, 16, 17 

meal, poisoned, as bait for sugar-beet wireworm 60 

poisoned, as bait for sugar-beet wireworm 60 

Creosote, coal-tar. (See Cresol.) 

Cresol against sugar-beet wireworm 52, 57-58 

Culture, clean, against sugar-beet wireworm adults 61-64 

Dock. (See Rumex hymenosepalus.) 

Drasterius livens, in sugar-beet fields, comparison with Limonius californicus. . . 12, 13 
6140°— Bull. 123—14 5 65 



66 THE SUGAR-BEET WIREWORM. 



Early planting against sugar-beet wireworm 61 

Elaterids in sugar-beet fields, comparison with Limonius caUJornicus 13 

Euphagus cyanocephalus, enemy of Limonius cali/omicus beetles 47 

Flycatcher, ash-throated. (See Myiarchus cinerascens cinei'ascens.) 

Fungous diseases of Limonius cali/omicus 47-48, 49-50 

Grass, Johnson. (See Sorghum halepense.) 
Ground-beetles. {See Carabidae.) 

Guano fertilizer against sugar-beet wireworm 61 

Gull, sea. (See Larus sp.) 

Insects found with Limonius cali/omicus 12-13 

Johnson grass. (See Sorghum halepense.) 

Kerosene against sugar-beet wireworm 52, 54, 55 

emulsion against sugar-beet wireworm - 52, 54r-55 

Killdeer. (See Oxyechus voci/erus.) 

Lanius ludovicianiis gambeli, enemy of Blapstinus sp 46 

Limonius cali/omicus beetles 46, 47 

Larus sp.. enemy of Limonius cali/omicus 48 

Lead chromate against sugar-beet wireworm 52, 58, 60 

Limonius cali/omicus, adult, ability to withstand unfavorable conditions 40 

activity, beginning of period 33-34 

appearance in spring 33 

cages used in rearing 36,37 

description 14 

duration of life under varying conditions 37-38 

effect of temperature thereon 39, 40 

emergence 32 

actions thereafter 41^2 

period 32 

endurance when submerged in water 38 

life history and habits 32-42 

mating 40-42 

actions thereafter 41-42 

oviposition 42 

variation 34^35 

adults from emergence to hibernation 42-43 

bibliography 64 

classification 13 

control, natural 46-50 

descriptions of stages 14—16 

distribution 16 

, dissemination 45, 46 

egg, description 14 

length of stage 20 

life history 18-20 

time and place of deposition 18-19 

eggs, number and hatching 19-20 

emergence from hibernation gradual 43^4 

enemies and checks 46-50 

food plants 16-17, 35-36 

iungi affecting pupae and eggs 49-50 

habits and life history 18-42 

hibernation 43 

"secondarv " 33, 44-45 



INDEX. 67 



Lhnonius cali/ornicus, historical 11 

injury to beets 26-27, 29 

insects found therewith 12-13 

larva, description 14-15 

duration of life wdthout food 27-28 

emergence from egg 20 

habits 22-26 

injury to beets 26-27 

length of stage, approximate 24 

life history and habits 20-30 

molting 29-30 

newly hatched 20-21 

rearing cages used 21-22 

relation between size and abundance and injury 

in beet fields 29 

life cycle, approximate length 42 

history and habits 18^2 

losses due to work 11-12 

mating 40^1 

mortality during hibernation 43 

names, common 13 

occurrence of beetles in field 45 

oviposition 42 

pupa, changes in color 31 

description 15-16 

length of stage 31 

life history 30-31 

vitality 31 

pupal cell 30 

pupation 30-31 

remedial measures 50-64 

deterrents against larvae, experiments 52-60 

fall plowing for destruction of pupae . . 51 

historical 50 

poisoned baits 50-51 

seasonal history , 42-46 

soil conditions affecting pupation 30-31 

summary 64 

synonymy 13 

Lophortyx cali/ornicus vallicola, enemy of Limonius cali/ornicus 47 

Meadowlark, western. (See Sturnella neglecta.) 
Medicago spp. (See Alfalfa.) 
Mustard. (See Brassica niger.) 

Myiarchus cinerascens cinerascens, enemy of Limonius cali/ornicus 47 

Nettle, food plant of Limonius cali/ornicus 16 

Nicotine, free, solution, against sugar-beet wireworm 52, 57 

sulphate against sugar-beet wireworm 52, 57 

Nigh thawk, western. (See Chordeiles virginianus henry i.) 

Oxyechusvoci/erus, enemy of Limonius cali/ornicus 47 

Paris green in poisoned baits against sugar-beet wireworm 51, 60 

■ Pigweed. (See Amaranthus retroflexns.) 

Platynus sp. in sugar-lieet fields with TAmonius cali/ornicus 13 

Potassium cyanid and flour in poisoned baits against sugar-beet wireworm 60 



68 THE SUGAR-BEET WIREWORM. 



Potassium cyanid, solid , against sugar-beet wireworm 52, 59-60 

solution against sugar-beet wireworm 52, 59-60 

sulphid solution against sugar-beet wireworm 52. 58 

Potato, food plant of Limonius californicus 16. 17 

Quail, valley. (See Lophortyx californicus vallicola.) 

Rumex hymenosepalus , food plant of Limonius californicus 16 

Salt solution against sugar-beet wireworm 52, 58 

Shrike, California. (See Lanius luclovicianus gambeli. ) 

'"Skipjacks, "colloquial name for Elateridse 13 

Soap, whale-oil, against sugar-beet wireworm 52, 55 

Solanum tuberosum. {See Potato.) 

Sorghum halepense, food plantof Limonius californicus 16, 35 

Sparrow, native, enemy of Limonius californicus beetles 47 

'■ Spring-beetles, ' ' colloquial name for Elateridee 13 

Storms as checks to Limonius californicus beetles 47 

Strychnine in poisoned bait against sugar-beet wireworm beetles 51, 60 

Sturnellaneglecta, enemy oi Limonius californicus beetles 47 

Sugar-beet wireworm. (See Limonius calif ornicus .) 

Sulphur, dry, against sugar-beet wireworm 52, 58 

Tar water against sugar-beet wireworm 52, 55-56 

Temperature as affecting ndult Limonius californicus 39 

Turpentine against sugar-beet wireworm 52, 53-54 

Variationinbeetlesof Li/noni«sca/i/b/'nic(is 34-35 

Wireworm, lesser sugar-beet, undetermined species nea.x L. californicus 13 

Wireworms found in sugar-beet fields 12-13 



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